1939: Zoology

In reviewing the researches in the field of zoology for the past year it is impossible to mention more than briefly a few of the studies which have held the attention of scientists. Both experimental and descriptive or observational studies have yielded some interesting discoveries.

Sexual Studies and Hormones.

In the specialized field of endocrinology the most outstanding researches seem to have been directly or indirectly concerned with the problems of sex and reproductive physiology. Doctors Bachmann, Cole and Wilds, chemists of the University of Michigan report the total synthesis of the female sex hormone equilenin. This name was originally given because it was first found in the urine of pregnant mares. This synthesis can be considered an important advancement in the study of sexual activity in the female.

Dr. R. T. Hill of the Indiana University Medical School reported an interesting case of sex reversion in the goat. The animal was obviously a female when born. Shortly after birth indications of an abnormality were present and at the age of 8 months the goat was found to have male sex glands developing in the region where anatomically the ovaries should be. This is another example of the relatively close relationships between the female and male sexes at an early developmental stage.

Doctors Gaunt and Hays of New York University and Princeton University have reported that crystalline progesterone, the hormone normally found in the ovary and primarily concerned with reproduction, is also capable of maintaining life of animals deficient in the hormone found in the adrenal glands or cortin. Workers from other institutions have also repeated and confirmed the above work during the past year. This observation is not so surprising when one considers the chemical analysis of these hormones from the ovaries and adrenals and finds them to be somewhat similar chemically.

Sex control at the will of the investigator has been demonstrated by Dr. W. A. Puckett of Princeton University. However, this control has been applied to amphibians and it is doubtful whether it could be extended to the higher vertebrates and especially the human. Nevertheless, the procedure worked out by Dr. Puckett has worked very well in the bullfrog. He subjected the young frog or tadpole to injections of female hormone, theelin, or the male hormone, testosterone, in combination with an extract from the pituitary gland and found that all tadpoles would be rushed to maturity and that the sex ratio of the injected group would depend directly on the number injected with either the male or the female sex hormone.

Experiments in Embryology.

In the field of experimental embryology several interesting experiments have been carried out. Dr. L. H. Hyman of the American Museum of Natural History has continued her work on the problem of regeneration in invertebrates. By her experiments she has shown that the ability to regenerate lost parts is very intimately associated with the nervous system and furthermore that there is an anterior-posterior gradient to regeneration. For example, the potentiality to form a new head is greatest when the worm is severed near the head region. However, the farther the cut is made posteriorly toward the tail the more difficult it becomes to form a head for the cut then comes to lie in the region which is tail-dominated. On the basis of this experiment one has to then consider also a posterior-anterior gradient for tail regeneration.

It is well known that most parasites go through a number of stages from the larval to the adult for the completion of their developmental cycle. However, it is sometimes difficult to secure all of the stages because a number of different hosts are sometimes needed to show the complete cycle and if some of the intermediate hosts are unknown the cycle is not complete. The past year Doctors R. W. Glaser and N. R. Stoll of the Rockefeller Institute for Medical Research at Princeton, N. J., have reported successful in vitro cultivation of a parasitic worm of sheep. By raising these parasite eggs in a sterile culture medium in test tubes they were able to hatch and carry the worms through their two free-living stages. They have not as yet succeeded in finding a nutrient medium which will enable them to raise the adult worms but investigations are being continued in that direction. Nevertheless their work must be considered another step toward a better understanding of parasites harmful to man as well as animals.

Another interesting study which can also be considered embryological, is the successful grafting of the embryonic limb of a white leghorn chick onto the body of a turkey embryo. Dr. H. L. Eastlick of the University of Missouri carried out the above experiment which was intended to be a reciprocal grafting experiment where the turkey limb was also grafted to the leghorn chick body. However, the latter graft was unsuccessful. Nevertheless, the first part of the experiment resulted in the white leghorn engrafted limb assuming the host or turkey characteristics. This experiment is a further confirmation of the fact that host inducing properties can be acquired by the donor if environmental conditions are suitable.

Artificial Activation of the Ovum.

On studies concerned with the early development of the egg, Dr. G. Pincus of Clark University, who is already well recognized for his work on the artificial activation of the rabbit ovum, has continued his studies on the human egg or ovum. He is primarily interested in studying the early stages of development so that medical knowledge, which is now most incomplete for the early stages, will be bettered. He secures the eggs from ovaries which have been removed by surgical operation for other reasons, and attempts to stimulate them into starting on their initial developmental path.

Observations by Government Bureaus.

In the more strictly observational field of zoology a number of interesting studies have been made. Zoologists of the U. S. Department of Agriculture have reported that moles, which have often been blamed for eating plant roots and bulbs, are not, for the most part, vegetarians, but rather feed on underground insects and grubs. They report that the short-tailed pine mouse makes use of the mole runway and since these animals are true vegetarians, they should shoulder most of the blame for the destruction often attributed to the mole.

V. L. Loosanoff, of the U. S. Fisheries Biological Laboratories reports observations on the spawning of oysters which tends to break down an old doctrine in the oyster industry. It has always been thought that oysters would not spawn at water temperatures below 68° F. However, Mr. Loosanoff has found spawning activity in water with temperatures as low as 62° F. It is entirely possible that spawning may occur at even lower temperatures when other environmental conditions are suitable.

Changes in Habit Due to Environment.

It has been reported that American large-mouth black bass are very numerous in a lake in Kenya Colony, Africa. It has been found that they grow faster and reach a larger size than do similar fish of the same age taken from lakes in Illinois and Wisconsin. It has been suggested that this increase in growth and weight of the African series might possibly be due to the restricted competition for food known to exist in African lakes.

Studies in Genetics.

Studies in the field of genetics have continued with better cytological techniques being devised for the study of chromosomes and also of the genes or hereditary units in chromosomes in a number of animal forms. Dr. C. A. Berger of Woodstock College has described a most interesting condition in the cells lining the digestive tract of a mosquito larvae. He finds the chromosome complement of individual cells in this area increasing one to two hundred times the normal without any division of the cells being observed. Then, when the larvae prepare to change into the adult form, the cell divisions all occur simultaneously and the normal chromosome complement characteristic of the species is then brought back to the new cells.

While genes have usually been considered as the units which are influential in determining the eye color in Drosophila or fruit flies, Dr. E. L. Tatum of Stanford University has reported evidence which seems to indicate that bacteria are also able to change the eye color. He states that the change from white to brown color is brought about by a hormone produced by the bacteria. This hormone then works in conjunction with tryptophane, an amino-acid added to the diet of the fly. The bacterium producing this hormone has not as yet been described as a distinct species. See also BIOLOGY; ENTOMOLOGY.