Parturition Period Research Articles

Notes on the Bull shark Carcharhinus leucas in the lagoon region of Cananéia, Brazil

Ninety one young specimens and 3 adult females of BulI shark ("cação cabeça chata") caught in the lagoon region of Cananéia were examined, their tooth formula being 27/25 and the number of pre-caudal vertebrae ranging from 109 to 115. The proportion between the 1st and 2nd dorsal fins were found to be 2.3 and 2.8 for the young,and 2.9 to 3.1 for the adults. These data confirm that the studied form belongs to C. leuoas. Young occur regularly but in limited numbers.As regards the adults, however, females only appear during the short parturition period, i.e., from November to February. The number of embryos in the litters were from 7 to 9, their sizes ranging between 768-812 mm. The length of the smallest free young found was 697 mm, but young presumably 9 to 12 months old had 98 to 112 cm; between 21 and 24 months they were reaching 124 to 128 cm, that is, the same size they have when they start migrating to the open sea. The feeding inhibition phenomenon during the period of parturition was not observed in the female specimens caught in the lagoon. The more abundant species found in the stomach contents were: Arius spixii; Chloroscombrus chrysurus; A. grandicassus; A. barbus; Felichtys marinus; Genidens genidens; Chanophorus tajacica and Carcharhinus porosus.

Additional notes on the parturition period of the Japanese harvest mouse, Micromys minutus japonicus, in Kyushu

Additional notes on the parturition period of the Japanese harvest mouse, <I>Micromys minutus japonicus</I>, in Kyushu

Observations on Abnormalities of Parturition in Captive Bottle-Nosed Dolphins, Tursiops truncatus, and Concurrent Behavior of Other Porpoises

Two females experienced difficulty while in labor. One birth resulted in cephalic presentation. The dominant bull's behavior underwent abrupt change during the parturition period. The abnormal birth and breathing at birth are discussed.

Tooth Development and Wear in Myotis

the end of the parturition period, it reveals the changes that occur in the deciduous dentition. The immature animals of the collection ranged in age from a few days to approximately 50 days (Stegeman, 1954). The deciduous teeth are shed during this period and the permanent dentition acquired. The number of specimens and the conditions under which they were obtained makes them meet most of the requirements set forth by Andersen (1918) for the determination of age, namely: (1) All specimens collected at one time; (2) All specimens collected from the same area; (3) A large series; and (4) Animals separated by one year of age. Since the skulls of adults were collected on a single date they can be separated into yearly groups more readily. Methods. -After the specimens were weighed, measured, and sexed the heads were severed, with the fur and flesh left on, each wrapped in a small square of cheesecloth, and a numbered tag attached. They were then dried and stored for future study. Several attempts were made to cook and clean these skulls without success. They were too fragile and came apart during the cleaning operation. A group was then exposed to dermestid larvae with no better success, since the larvae ate bones and all, particularly the immature specimens. The group was next infected with the larvae of the common clothes moth Tineola bisselliella (Hum.). These larvae were so small that they did not destroy the bones. Random samples were examined at intervals until the specimens were sufficiently clean to determine the condition of the teeth. The loosened tissues and frass were then removed and the examinations made under a binocular dissecting microscope. The deciduous teeth of each immature animal were listed and the total number recorded. The skulls were then classified on the basis of the number of milk teeth present. The skulls of mature bats were examined for tooth wear and grouped

The Determination of Age of Nestling and Sub-Adult Gray Squirrels in West Virginia

The inspection of den trees, boxes and leaf nests in order to ascertain the peak parturition period of the gray squirrel, Sciurus carolinensis, has been undertaken by almost every investigator studying this species. Due to the difficulty in finding litters, none has published any work that can be used as a basis for age determination. The writer has found, however, the work of Monica Shorton (1951) in Great Britain to be outstanding. Table 1 is based on her work and the additional data on 68 nestling squirrels of varying ages collected during the present study. All data pertaining to nestling squirrels were collected on Seneca State Forest, located in the Allegheny Plateau Region of West Virginia. Data on the sub-adults (squirrels over 10 weeks old) were collected on Seneca and six other state forests and refuges located throughout the State. Fifty-one nestlings (19 litters) were checked once, nine (three litters) twice, six (two litters) four times and two (one litter) six times. The checks were made at intervals of one to three weeks. Repeated visits were made to all litter sites, but in the majority of cases the litters were not present the second time. Data were also collected from nestlings born in captivity. In these cases the mother usually devoured her young after they had been handled several times. Notes were taken on the condition of the pelage, eyes, ears and teeth at each examination. Measurements of the hind foot, body and tail length were also taken and each squirrel was weighed. While the key was developed on the basis of the data obtained from the squirrels found in the spring and summer of 1953, it was applied again to the squirrels found during the spring of 1954. Some corrections and additions were made after the latter check. It was found that the key applied in the majority of cases, but occasionally one of the characteristics would not fall in the same age class as the others; however, in most instances, five of the seven criteria were valid. Spring litters in 1954 were larger than in 1953. It was found that one runt was present in the majority of cases where there were four squirrels in the litter. Data on these runts were not used in devel-

Studies on the life cycle of the snail, Viviparus contectoides

AbstractMore than 3700 individuals of Viviparus contectoides from the Illinois River, near Peoria, Illinois, and from the Erie Canal in central New York, have been the subject of statistical and biological analysis as periodic quantitative samples to secure information on the life cycle. Sexes are easily distinguished through tentacular differences. Shells show marked sex dimorphism of size. Males reach a maximum height of 25 mm.; females may exceed 40 mm. Distribution curves, checked by experimental data on another species of the same genus, give evidence that males live normally about one year, while females may live three years. Differences in sex ratio are attributable to differences in life span and to changes in environmental factors producing aggregations of members of one sex.In central New York, the parturition period seems to begin to March and terminates in June. In central Illinois it extends from February into May. The uterus of a gravid female contains eggs, embryos, and shelled young in a graded series. At birth, the young shell contains one and one‐half whorls and has a height of approximately 3.8 mm. Color bands are present on the shell three months before birth. Initial growth rate is extremely rapid. In less than three months the largest of the new generation are as large as the smallest of the parent generation. Graphs given show seasonal changes in the population.