Pseudacris Triseriata Research Articles

The Rate of Metabolic Temperature Acclimation in the Frog, Rana temporaria

Previous articleNext article No AccessThe Rate of Metabolic Temperature Acclimation in the Frog, Rana temporariaMikko N. E. HarriMikko N. E. Harri Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 46, Number 2Apr., 1973 Article DOIhttps://doi.org/10.1086/physzool.46.2.30155595 Views: 9Total views on this site Citations: 19Citations are reported from Crossref Journal History This article was published in Physiological Zoology (1928-1998), which is continued by Physiological and Biochemical Zoology (1999-present). PDF download Crossref reports the following articles citing this article:E S Savelieva INVESTIGATION OF INSULIN-, GLUCAGON-, SOMATOSTATIN-POSITIV CELLS LOCALIZATION IN THE LANGERHANS’ ISLENDS IN DIFFERENT PERIODS OF BIOCYCLE OF ANURA, I.P. Pavlov Russian Medical Biological Herald 21, no.11 (Dec 2013): 7–10.https://doi.org/10.17816/PAVLOVJ201317-10Ari J Tiiska, Kari Y.H Lagerspetz Effects of thermal acclimation on nervous conduction and muscle contraction in the frog Rana temporaria, Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 124, no.33 (Nov 1999): 335–342.https://doi.org/10.1016/S1095-6433(99)00125-7Donald G Dunlap The effects of differing photoperiods during thermal acclimation on oxygen consumption in the hylid frogs, Acris crepitans and Pseudacris triseriata, Comparative Biochemistry and Physiology Part A: Physiology 94, no.33 (Jan 1989): 519–523.https://doi.org/10.1016/0300-9629(89)90132-1Loren U. Williamson, James R. Spotila, Edward A. Standora Growth selected temperature and CTM of young snapping turtles, Chelydra serpentina, Journal of Thermal Biology 14, no.11 (Jan 1989): 33–39.https://doi.org/10.1016/0306-4565(89)90027-2E.Don Stevens Acclimation temperature markedly alters the motivation to feed in the toad, Bufo americanus, Journal of Thermal Biology 13, no.22 (Apr 1988): 73–78.https://doi.org/10.1016/0306-4565(88)90015-0E. Don Stevens The effect of acclimation temperature on feeding performance in the toad, Bufo americanus, Comparative Biochemistry and Physiology Part A: Physiology 89, no.22 (Jan 1988): 131–135.https://doi.org/10.1016/0300-9629(88)91069-9Martin E. Feder Acclimation to constant and variable temperatures in plethodontid salamanders—I. Rates of oxygen consumption, Comparative Biochemistry and Physiology Part A: Physiology 81, no.33 (Jan 1985): 673–682.https://doi.org/10.1016/0300-9629(85)91046-1Martin E. Feder, Allen G. Gibbs, Gerard A. Griffith, Joyce Tsuji Thermal acclimation of metabolism in salamanders: Fact or artefact?, Journal of Thermal Biology 9, no.44 (Oct 1984): 255–260.https://doi.org/10.1016/0306-4565(84)90005-6 Martin E. Feder Metabolic and Biochemical Correlates of Thermal Acclimation in the Rough-Skinned Newt Taricha granulosa, Physiological Zoology 56, no.44 (Sep 2015): 513–521.https://doi.org/10.1086/physzool.56.4.30155874G.D. Parry The influence of the cost of growth on ectotherm metabolism, Journal of Theoretical Biology 101, no.33 (Apr 1983): 453–477.https://doi.org/10.1016/0022-5193(83)90150-9Katsuji Tsugawa Effects of cold acclimation on the standard metabolic rate and osmotic fragility of erythrocytes in an aquatic anura, Xenopus laevis, Comparative Biochemistry and Physiology Part A: Physiology 73, no.33 (Jan 1982): 431–436.https://doi.org/10.1016/0300-9629(82)90180-3Martin E. Feder Environmental variability and thermal acclimation of metabolism in tropical anurans, Journal of Thermal Biology 7, no.11 (Jan 1982): 23–28.https://doi.org/10.1016/0306-4565(82)90015-8J. De Costa, M. Alonso-Bedate, A. Fraile Temperature acclimation in amphibians: Changes in lactate dehydrogenase activities and isoenzyme patterns in several tissues from adult Discoglossus pictus pictus (Otth.), Comparative Biochemistry and Physiology Part B: Comparative Biochemistry 70, no.22 (Jan 1981): 331–339.https://doi.org/10.1016/0305-0491(81)90053-5Elizabeth Sherman Cardiovascular responses of the toad Bufo marinus to thermal stress and water deprivation, Comparative Biochemistry and Physiology Part A: Physiology 66, no.44 (Jan 1980): 643–650.https://doi.org/10.1016/0300-9629(80)90012-2K.Y.H. Lagerspitz Interactions of season and temperature acclimation in the control of metabolism in Amphibia, Journal of Thermal Biology 2, no.44 (Dec 1977): 223–231.https://doi.org/10.1016/0306-4565(77)90035-3Richard H. Shertzer, Robert G. Hart, Frank M. Pavlick Thermal acclimation in selected tissues of the leopard frog Rana pipiens, Comparative Biochemistry and Physiology Part A: Physiology 51, no.22 (Jun 1975): 327–334.https://doi.org/10.1016/0300-9629(75)90377-1Mikko N.E. Harri Effect of season, temperature acclimation and starvation upon plasma FFA and glycerol levels in the frog, Rana temporaria, and in the toad, Bufo bufo, Comparative Biochemistry and Physiology Part B: Comparative Biochemistry 50, no.44 (Apr 1975): 531–534.https://doi.org/10.1016/0305-0491(75)90083-8M.N.E. Harri, A. Talo Effect of season and temperature acclimation on the heart rate-temperature relationship in the frog, Rana temporaria, Comparative Biochemistry and Physiology Part A: Physiology 50, no.33 (Mar 1975): 469–472.https://doi.org/10.1016/0300-9629(75)90302-3Mikko N.E. Harri The relation between thyroid activity and responsiveness to adrenaline during cold acclimation in the frog, Rana temporaria, Comparative and General Pharmacology 5, no.3-43-4 (Jan 1974): 305–309.https://doi.org/10.1016/S0010-4035(74)80017-0

A Study of the Western Chorus Frog, Pseudacris triseriata, in Vigo County, Indiana

An ecological study was conducted on the Western Chorus Frog, Pseudacris triseriata, at Terre Haute, Vigo County, Indiana, between 1963 and 1969. Descriptions of adults are given with comparisons between sexes and ponds. Descriptive information is included on the development of tadpoles, froglets, and young individuals. Data on breeding congresses, incubation periods and food habits are presented. The relation of P. triseriata to Hyla crucifer, Natrix sipedon and Thamnophis sauritus is discussed. P. triseriata contained trematodes and nematodes. Eggs were generally laid in March or April at Terre Haute (12 March-22 April) and usually coincided with major rainstorms. In any one year most egg laying occurred over a relatively short period or periods. The number of eggs ranged from 12 to 245 in 96 masses (mean of 79.8). The total complement of eggs varied in 10 females from 440 to 752 (mean of 597.33). Water temperature affects the incubation period. In 1965, eggs in the field hatched in 8 to 13 days, while in 1969, during a colder period, eggs hatched in 15 to 27 days. In temperature control chambers at 44 degrees, eggs hatched between the 25th and 46th days, while nearly all eggs at 73 F hatched on the fourth and fifth days. The time from egg laying to metamorphosis, in one group of eggs in the field in 1965, took 52 days and in 1969, about 70 days. Metamorphosis at Terre Haute occurred in late May or early June. P. triseriata and Hyla crucifer occupied the same breeding ponds at the same time. Pseudacris would often sing both day and night, Hyla only at night. The two species were often segregated in individual breeding ponds. P. triseriata tadpoles were most abundant in water 11 to 22 cm deep and where emergent vegetation was less dense. There was no relation between tadpoles and distance to shore or presence or absence of Hyla crucifer tadpoles. P. triseriata tadpoles fed mostly on filamentous and non-filamentous algae. Metamorphosing individuals did not feed. Recently transformed froglets fed on Collembola, mites, small insects, and possibly shed skin. Individuals collected in summer and fall from terrestrial habitats fed on various invertebrates with ants and spiders being the most important. Adults of P. triseriata in the breeding ponds, unlike those of Hyla crucifer, fed, with lepidopterous larvae, spiders, curculionids, and chironomids being some of the important items utilized. Vegetation was also important. P. triseriata is a terrestrial rather than an aquatic feeder. Natrix sipedon was listed as a predator and Thamnophis sauritus as a probable predator on Pseudacris. A total of 291 (40.9%) of the male frogs, and 46 (28.3%) of the females yielded trematode parasites, a new species in the genus Glypthelmins currently being described by Robert E. Geyer. Of male frogs, 48.6% contained nematodes (Oswaldocruzia sp. and Aplectana sp.), as did 44.0% of the females. The average number of trematodes per frog was 7.2 in males and 3.9 in females, and for nematodes similar figures were 1.7 in males and 1.5 in females.

Boreal Chorus Frogs (Pseudacris Triseriata) Breeding in the Alpine in Southwestern Colorado

Boreal Chorus Frogs <i>(Pseudacris Triseriata)</i> Breeding in the Alpine in Southwestern Colorado

Boreal Chorus Frogs (Pseudacris triseriata) Breeding in the Alpine in Southwestern Colorado

Boreal Chorus Frogs (Pseudacris triseriata) Breeding in the Alpine in Southwestern Colorado

Studies on the Helminth Fauna of Iowa. I. Trematodes of Amphibians

A survey of 542 amphibians collected during 1953-1967 from 40 areas of northwest Iowa reveals an incidence of 52.8% infection with digenetic trematodes. Almost all represent new locality records. Hosts examined include Ambystoma tigrinum (Green), Bufo americanus Holbrook, Bufo cognatus Say, Acris crepitans Baird, Hyla versicolor LeConte, Pseudacris triseriata (Wied), Rana catesbeiana Shaw, and Rana pipiens Schreber. Fifteen species of flukes are included in the collection, 14 of which are harbored by Rana pipiens (leopard frog), the most abundant host in the region. A summary of pertinent literature relating to each species of trematode. is presented, together with 20 illustrations. The trematode fauna of amphibians of the United States is quite varied and has been the subject of numerous investigations. Early compilations by Stiles and Hassall (1894) and by Pratt (1900, 1904) were followed by the first comprehensive systematic accounts of Stafford (1902a,b, 1905), who published several reports on helminths of North American vertebrates. Later studies on amphibian helminths from the United States include those by Cort (1912, 1915a), Harwood (1932), Brandt (1936), Ingles (1936), Rankin (1937), Manter (1938), Kuntz (1940), Parker (1941), Kuntz and Self (1944), Rankin (1945), Bouchard (1951), Lehmann (1954, 1956, 1960), Odlaug (1954), Najarian (1955), Frandsen and Grundmann (1960), Waitz (1961) and Campbell (1967). Pratt and McCauley (1961) compiled an annotated catalogue of the trematodes of the Pacific northwest. A series of abstracts and papers published by Walton (1942-1962)1 included a worldwide compilation of amphibian hosts, parasites and their geographic distribution. This information, together with a comprehensive bibliography, was published in microcard form in 1964. The herculean effort of Yamaguti (1958) to bring together an account of all genera of digenetic trematodes of vertebrates has provided a useful summary of the literature up to 1955. Published accounts of the helminth fauna of Iowa are regrettablv meager. Since 1953, an extensive survey of helminths of vertebrates within the state has been under way and has resulted in the examination of several thousand hosts. This report, the first in a series devoted to the helminths of Iowa vertebrates, is concerned with trematodes of amphibians, particularly those from the lakes region of northwestern Iowa. 1 For a listing of these reports, see the U.S. Dep. Agriculture Index Catalogue of Medical and Veterinary Zoology, Part 17 (1952) (Authors) and subsequent supplements.

Montane and piedmont chorus frogs (Paeudacris triseriata): metabolic rate as a function of temperature.

Die Stoffwechselraten von Froschen (Pseudacris triseriata) aus Tiefland- und Bergpopulationen wurden bei 10 ‡C und 20 ‡C bestimmt. Die beiden Populationen unterschieden sich nicht signifikant in der Stoffwechselrate bei den 2 Testtemperaturen.

COMPARATIVE REPRODUCTIVE BIOLOGY OF MONTANE AND PIEDMONT CHORUS FROGS

Sub-units of a species living in contrasting environments may respond to differences in their respective habitats by developing differentially adaptive traits. For example, Moore (1942, 1946, and 1949) has demonstrated differences in both developmental temperature tolerances and coefficients between northern and southern populations of R. pipiens. Also, Ruibal (1955) has shown that populations of R. pipiens from different elevations in Mexico exhibit different rates of development at all temperatures tested. Embryos from higher elevations develop more slowly than their lowland counterparts. Ruibal suggests that this difference may be due to a history of selection for rapid development in the lowland localities resulting from greater interspecific competition in the larval stage. This phenomenon, called special adaptation by Brown (1958), may be most conveniently elucidated by comparing different conspecific local populations which are geographically proximate, thus minimizing the effects of differentiation due to isolation by distance. An opportunity to study this mechanism under near optimal conditions is afforded by populations of the boreal chorus frog, Pseudacris triseriata (Weid), in northern Colorado. In this area populations of P. triseriata occur at elevations from less than 4900 ft to above 10,000 ft. A presumed result of this elevation gradient has been the development and maintenance of numerous differences between montane and and piedmont chorus frogs. Variations in body size, adult temperature tolerance, and metabolism have been described in a previous paper (Pettus and Spencer, 1964). The purpose of this paper is to report our observations on variations in the eggs of these frogs and the results of a series of experiments designed to reveal differences in temperature effects during development. Both Moore (1949) and Ruibal (1955) have reported geographic variation in egg size of Rana pipiens. Moore's data show, with one striking reversal, a correlation between increased egg diameter and increased latitude. Ruibal reported only minor variation in egg diameters in spite of the fact that his samples were drawn from populations over a wide range of elevations.

Size and Metabolic Differences in Pseudacris Triseriata (Anura) from Different Elevations

An altitudinal cline in body size is described. Frogs from higher elevations are larger than those from prairie populations. Oxygen consumption per unit of body weight is shown to be inversely related to size. The ecological relation- ships of these two parameters and their possible adaptive significance are discussed. The phenomenon of geographic variation has been so amply illus- trated by the description of numerous subspecies that it has come to be expected in any wide-ranging species. However, too little attention has been given the mechanisms responsible for generating the observed variations. This report summarizes some of the differences found in populations of the chorus-frog Pseudacris triseriata (Weid) occurring at different elevations in northern Colorado and includes certain pre- liminary data from experiments designed to determine the adaptive significance of the observed differences. Perhaps the greatest contrast between populations from different elevations in the area studied is in body size. This trait together with its relationship to oxygen consumption will be the major topics of this paper, but other striking differences have been found. There are highly significant differences in egg size, number and color, as well as adult coloration and larval developmental. The latter three cate- gories will be discussed in later papers. The present study is similar to those of Moore (1942, 1949) and Ruibal (1955, 1957) in that frogs from contrasting environments have been compared in an attempt to find differentially adaptive charac- ters. A major difference is in the distance involved. While Moore and Ruibal compared populations living hundreds of miles apart at the extremes, this study has been primarily concerned with popula- tions separated by only 40 miles. This difference should be of impor- tance if, in fact, distance alone may deter gene flow between popula- tions. It should however be noted that since different species with presumably different dispersal abilities are being considered, statute

Hearing and Responses To Calls in Anurans

Abstract1. Nerve responses evoked by tone pips of known frequency were recorded from the medulla of Bufo americanus, Rana pipiens, Rana clamitans, Pseudacris triseriata, and Hyla crucifer. 2. Nerve responses were obtained between 20 cps and 4000 cps in Bufo and Rana, and between 100 cps and 6000 cps in Pseudacris and Hyla. 3. In all species, the best frequency for nerve responses was 1000 cps. In Pseudacris and Hyla there was a second low threshold area at 2000-3000 cps. It is suggested that the lower frequency dip in the response curve may represent responses from the pars amphibiorum and that the higher frequency dip may represent responses from the pars basilaris. 4. The threshold at the best frequency in Rana is similar to the sensitivity of human hearing. 5. Three Pseudacris and one Hyla were induced to answer tone pips. 6. These answered pips of frequencies between 700 cps and 4600 cps. Since this conforms to the high frequency dip in the nerve response curve, it is suggested that the Hylids might have been hearing pips with the pars basilaris only. 7. Pseudacris answered pips of a great variety of durations and intervals. 8. The data suggest that responses of Pseudacris males to frog calls may be, to a great extent, non-specific. 9. Alternating of calls in duets is controlled by at least two factors. There is a constant latency between a call and the stimulus eliciting it. A stimulus following a call too closely inhibits calling. 10. The data obtained here and by others suggest that even for location of males by females, the repetitive nature and frequency of calls may be of only minor importance. Rather, trill rate is implicated as an important call parameter.

A Behavioral Analysis of the Mating Call of the Chorus Frog, Pseudacris triseriata

In the laboratory, 156 Pseudacris triseriata reacted to a choice of two calls; some were unaltered natural calls, others were electromechanically constructed. The results of these tests show that female P. triseriata respond to a wide variety of auditory stimuli. Some outstanding characteristics of the call, for example, notes-their number, spacing and patterns of intensity and frequency, are not essential for the mating response of the female. In general, the most functional features of the call seem to be the following: harmonic qualities, duration of 0.50 to 0.75 sec, interval between calls about 1.0 sec, intensity approximately that of the natural call, frequency about 1,800-2,600 cps, continuous calling over several minutes and from the same general locus.

The Amphibia of Wayne County, Ohio

During the spring months of 1957-1962 and the academic year of 1959-1960, a survey of the amphibians of Wayne County, Ohio, was conducted. Collecting trips were initiated when ice began to melt on the ponds and were coordinated with spring rains. Trips to the more productive areas were made more often and collecting was more extensive and intensive in these localities (see Figure 1). The less productive areas proved to be in the southeastern part of the county, where local farmers have cleared the land surface extensively. Land not under cultivation is utilized as pasturage for livestock and has been stripped of woods and debris. Natural ponds contain little marginal vegetation suitable for even the smallest of local frogs Only the most ubiquitous amphibians have been collected in this part of the county. Eurycea bislineata and Desmognathus fuscus inhabit the streams and Rana pipiens, R. clamitans and Bufo americanus are undoubtably present. However, species which require woodlands, and the breeding ponds associated with them, can be expected to show spotty distributional patterns, if they are present at all. Specimens collected were placed in the museum of the Biology Department, College of Wooster (CW; Ur Urodela, An Anura) and the Museum of Zoology, The University of Michigan, Ann Arbor (UMMZ). For completeness, literature records of specimens not personally examined have been included. The following collections are represented: Ohio State Museum (OSM), Stone Laboratory, Ohio State University (SL), Cleveland Museum of Natural History (ZF), and Wilmington College (WC). A combination of all reports (Bishop, 1943; Walker, 1946; Conant, 1958) indicates that the following amphibians can be expected to occur in Wayne County. Taxa prefaced with an asterisk have not yet been taken: Necturus maculosus, *Cryptobranchus alleganiensis, Notophthalmus viridescens, *Ambystoma jeffersonianum, A. texanum, *A. opacum, *A. tigrinum, A. maculatum, Plethodon glutinosus, P. richmondi, P. cinereus, Desmognathus fuscus, Hemidactylium scutatum, *Gyrinophilus porphyriticus, Eurycea bislineata, E. longicauda, Pseudotriton ruber, Rana clamitans, R. sylvatica, R. pipiens, R. palustris, R. catesbeiana, Pseudacris triseriata, *Acris crepitans, Hyla versicolor, H. crucifer, Bufo americanus, B. woodhousei.

Vocalization as an Isolating Mechanism in Frogs

In laboratory tests, female Hyla crucifer selected the call of their own species in preference to that of Pseudacris triseriata, but not in preference to that of P. ornata. Female triseriata selected the call of their own species instead of that of the allopatric leptodactylid Eleutherodactylus portoricensis. On the other hand, only about 8 out of 10 succeeded when given a chance to respond to the calls of sympatric hylids-P. ornata, P. brachyphona and H. crucifer. Local P. triseriata females were unable to discriminate be- tween a call of a member of their own population and that of a frog recorded in New York; however, when given a chance to respond to a call recorded in Manitoba, 8 out of 9 reacted to the locally recorded call. Thus, for some species, vocalization is a major isolating mechanism, for others it is partially effective, and :for still others, it is ineffective. In those species in which vocalization is not a complete isolating mechanism, other factors-such as body size, rather small and subtle differences in behavior, habitat preference and timing-prevent interspecific matings. As is well known, optimum conditions for amphibian reproduc- tion are generally associated with rainfall. At such times, numerous individuals of several species often aggregate in the same pond. In these situations, it is important that interspecific matings be avoided. The latter result in gross biological inefficiency. Special secretions produced by the hedonic glands of males contribute greatly in pre- venting interspecific matings from occurring among most caudate amphibians. Among the Anura, such glands are absent. Numerous workers (Noble, 1931; A. P. Blair, 1941a, 1942; W. F. Blair, 1955, 1956; and many others) have stated that the calls of anurans serve to prevent crossing of the various species utilizing the same breeding site. However, there are no experimental data to verify this conclu- sion. With the recent observations that Pseudacris triseriata under- goes reproductive behavior in the laboratory and that the mating call alone guides a female to a particular male (Martof and Thomp- son, 1958), a method was provided for the testing of frog calls as an isolating mechanism.

Call Discrimination and Potential Reproductive Isolation in Pseudacris triseriata Females from Oklahoma

Call Discrimination and Potential Reproductive Isolation in Pseudacris triseriata Females from Oklahoma

Spring Emergence of the Western Chorus Frog

Spring Emergence of the Western Chorus Frog

Postglacial Dispersal of the Western Chorus Frog in Eastern Canada

Postglacial Dispersal of the Western Chorus Frog in Eastern Canada

Some Northern Limits of the Western Chorus Frog

Some Northern Limits of the Western Chorus Frog

QUANTITATIVE ASSAY OF THE MELANOPHORE DISPERSING HORMONE DURING THE DEVELOPMENT OF THE CHICKEN PITUITARY1

TWO OBSERVATIONS SUGGESTED the rather early appearance of the melanophore dispersing hormone during ontogeny. It was first called to our attention by the results of hypophysectomy of the Spring peeper (Pseudacris triseriata) embryos. In these forms the melanophores were easily distinguished and revealed complete concentration of pigment at a time when the control animals were hatching from their jelly envelopes. Secondly preliminary experiments showed that head extracts of recently hatched Rana pipiens larvae yielded considerable amounts of melanophoredispersing hormone when injected into hypophysectomised Anolis lizards, while the control body extracts gave a negative response. Histological examination of control pituitaries revealed no cytoplasmic differentiation. These observations suggested, not only the presence of the melanophore'dispersing hormone in the undifferentiated gland, but also revealed its functional rOle during very early development.

Description of the Larvae of Pseudacris triseriata and Bufo woodhousii woodhousii (Anura)

General Appearance.-Tadpole small, maximum total length before metamorphosis 30 to 32 mm.; tail tip obtuse, rounded; tail slightly attenuated toward tip; dorsal crest extended to about the vertical of the spiracle; spiracle sinistral, below lateral axis, directed backward and very slightly upward; spiracle opening round, the inner edge very slightly free from body; eye very slightly dorsal to lateral axis; anus dextral, opening about on the level of the ventral crest. Body uniformly and closely stippled with iridescent bronze; eyes closely stippled with bronze; body quite transparent; dorsal and ventral tail crests with finely scattered pigment areas, dark brown in color (preserved material); dorsal musculature of tail heavily pigmented, ventral musculature slightly less.

The phenomena of anuran metamorphosis. III. The development of the thyroid gland

AbstractThis paper presents a study of the growth and histological development of the thyroid in three species of frogs, the small Pseudacris triseriata, the large Rana catesbeiana and the intermediate Rana palustris. It was found that the history of the gland in relation to metamorphosis is essentially the same in all. Previous to metamorphosis the gland is small, and the cells very poor in cytoplasm. At the beginning of metamorphosis (i.e., rapid hind leg growth) the thyroid shows a marked acceleration of growth and activity, which continues and reaches a peak at the time of the emergence of the front legs. Late in metamorphosis a regression occurs.The conclusion is drawn that there is a rising concentration of thyroid hormone during the course of metamorphosis. The author has previously shown that such a rising concentration will induce the normal pattern as to sequence and time spacing of metamorphic events.The beginning of metamorphosis is conceived as dependent upon the time of stimulation of the thyroid and the pattern of its subsequent continuance as dependent upon the pattern of response of this gland.