Pond Animals Research Articles

PULL‐UP TRAP: A Quantitiative Device for Sampling Shallow‐Water Animals

A trap was designed for providing quantitative samples of freeswimming animals in marshes and shallow ponds. The device consists of netting tied to an aluminum frame with attachments for rapidly raising the net and entrapped organisms out of the water. Collections from a series of pull—up traps, operated monthly in Everglades National Park, provide an index of fluctuations in aquatic animal populations.

SOME PREDATORS OF AEDES STIMULANS (WALK.) AND AEDES TRICHURUS (DYAR) (DIPTERA: CULICIDAE) IN WOODLAND POOLS

The predators of first- and second-instar larvae of Aedes stimulans and A. trichurus in temporary woodland pools near Belleville, Ontario, were determined mainly by use of mosquito larvae tagged with radioactive phosphorus, but in part from the presence of aedine remains found in the digestive tracts of dissected beetles. Of 428 pond animals collected from the test pools 122 were found to be radioactive above background. Among the 17 species of aquatic insects and other animals that fed on mosquito larvae, 8 species of Dytiscidae, 1 of Hydrophilidae, 1 of Limnephilidae, and 1 pond snail are regarded as important predators. Three additional species of water beetles were identified as predators from aedine remains in their digestive tracts. The abundance of the predators, and the times of occurrence of six species in relation to mosquito development, are discussed.

THE CYCLIC NATURE AND MAGNITUDE OF CELL DIVISION IN GASTRIC MUCOSA OF URODELE LARVAE REARED IN THE POND AND LABORATORY

1. The mitotic rate of gastric mucosal epithelium in both pond- and laboratory-reared urodele larvae is cyclic over a 24-hour period. Maximum rate of cell division occurs in both groups between the hours of 10:30 A.M. and 12:30 P.M.; minimum mitotic activity is recorded between 6:30 A.M. and 8:30 A.M.2. In pond animals, the mitotic rate of gastric mucosa is 8 times the rate of the mucosa of laboratory-reared animals. The environmental differences between pond and laboratory are suggested as the underlying cause for the differential in the rates of mitosis in the two groups of animals. Since a similar difference was previously found in the epidermal mitotic rates of the same animals, it is suggested that in the pond environment an enhanced rate of growth is present.3. The difference between the pond and laboratory mucosal daily mean mitotic rate is of lesser magnitude than the difference between the epidermal rates of the same animals. This fact indicates that the epidermis may be responding directly to exogenous environmental factors, whereas the mucosa responds only to a lesser degree since it is not directly exposed to the environmental factors.

On the food, feeding mechanism and alimentary canal of Corixidae (Hemiptera, Heteroptera)*

SUMMARY. The food of corixids includes solid substances and is obtained partly from detritus, from algae including filamentous genera and to a lesser extent from free‐swimming pond animals, e. g. chironomids, tubifex etc. The methods of feeding can be summarized as follows:‐ (a) Detritus is “shovelled” to the tip of the rostrum by the palae and then sucked into the alimentary canal by the pharyngeal pump. (b) Algal filaments and free‐swimming pond animals are held by the palae, the stylets inserted, and the food, partly digested by enzymes secreted into it, is sucked into the alimentary canal. (c) The surfaces of stones, dead animals etc. are scraped with the palae, and the material so freed is sucked into the alimentary canal. The structure of the alimentary canal which presents several remarkable features is described. The unusual features to be seen are:‐ (a) the buccopharyngeal teeth; (b) the well‐developed proventriculus and the oesophageal valve; (c) the peritrophic membrane, formed in the presence of large quantities of food by delamination from a brush border. (a) The examination of the alimentary canal of Naucoris shows the presence of solid food, associated with which are pharyngeal teeth, and an oesophageal valve. The proventriculus is reduced and there is no peritrophic membrane. (b) The examination of the alimentary canal of Notonecta shows that only liquid food is present. There are no pharyngeal teeth, oesophageal valve, proventriculus nor is a peritrophic membrane present. The peritrophic membrane is to be regarded as a primitive feature because of its wide distribution including its presence in at least one annelid. Its formation in Melinna, in part from mucus, and the absence of the goblet cells in those regions of the gut in which it is found, indicates its fundamentally protective function. The nature of the food and the unusual features of the alimentary canals of corixids and naucorids, in particular the presence of the peritrophic membrane in Corixidae indicates that they are very primitive Hemiptera, the corixids more primitive than naucorids. Staining by special methods to demonstrate the Golgi apparatus and the presubstance, gives information as to which cells in the midgut are secretory in function. Two definite and two less certain methods of secretion are found. Definite (a) the production of non‐nucleate vesicles containing the enzymes; (b) the liberation of the enzymes unaccompanied by any part of the cell other than the dense lipoid containing substance which may adhere to the product. Less certain (c) the production of nucleate vesicles; (d) the disintegration into fine granules of part of the cell.