179 



SUMMARY Of CUERENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(principally invertebrata and cryptogamia), 



• MICROSCOPY, Etc.* 



ZOOLOGY. 

 VERTEBRATA. 



a. Embryolog-y, Evolution, Heredity, Reproduction, 

 and Allied Subjects. 



Individuality of Germ-nuclei in Cleavage Stages of Crypto- 

 branchus allegheniensis. — Bertra:^i G. Smith {Froc. Amer. Soc. 

 Zool. in Anat. Record, 1920, 17, 323). The germ-nuclei do not fuse in 

 fertilization. In the first cleavage mitosis each gives rise to a separate 

 group of chromosomes whose descendants pass separately to the daughter- 

 nuclei. During the ensuing resting stage each germ-nucleus is repre- 

 sented by a structurally distinct vesicle. Throughout early cleavage 

 the nuclear divisions are duplex, and the resting nuclei distinctly double. 

 The genetic continuity of each half of the double nucleus has been 

 clearly traced to an advanced cleavage stage, and even in the early 

 gastrula. But the double structure becomes increasingly disguised. 



J. A. T. 



Causal Factor in Hatching of Chick. — A. Gr. Pohlman {Aiiat. 

 Recorcl,^ 1919, 17, 89-104, 2 charts). Doubt is cast on Keibel's account 

 of the importance of the musculus complexus in causing the bill and egg- 

 tooth to strike forcibly against the shell. The musculus complexus does 

 attain a maximum development before and at the stage of hatching, and 

 shows a progressive atrophy after the chick is hatched, to the eighth 

 clay at least. But before the time of hatching the muscle is infiltrated 

 with lymph, which attains its maximum with the complete injection of 

 the yolk and the discharge of the allantoidal blood into the systemic 

 vessels. The infiltrated muscle is physiologically incapacitated from 

 pronounced muscular contraction, and one reason for the marked infil- 

 tration is undoubtedly its relaxed condition. The active muscular agent 

 in breaking the shell comes about through a change in the position of 



* The Society does not hold itself responsible for the views of the authors 

 of the papers abstracted. The object of this part of the Journal is to present 

 a summary of the papers as actually xmhlished, and to describe and illustrate 

 Instruments, Apparatus, etc., which are either new or have not been previously 

 described in this country. 



N 2 



