CHAPTER 8 



Embryonic Growth, in Animals 



8.1: Action on Gonads and Early Development 



Eggs have often proved to be an excellent material for colchicine 

 research, and in previous chapters results of work on various types 

 of eggs have been mentioned. Nuclear structure is modified in Tiibi- 

 jex,--- -3 the nuclear sap becomes granular in the Anodonta e^g,^^ 

 spindle changes are most evident in Arbaria^- '^'^ disturbances of 

 cleavage are noted in Spliaerechinus}' while curious surface changes 

 have been described in both Tiibifex-^^ and Arbacia.-*^ The size of egg 

 cells, their conspicuous spindle, and the possible induction of poly- 

 ploidy were factors making them useful in some of the early colchicine 

 research. It is remarkable, howe\er, that the first paper on this sub- 

 ject was written by two botanists.-''' 



We shall consider here only facts which have not been observed 

 in ordinary cells, and which are related to the special physiology and 

 cytology of eggs. Since there are few papers on modifications of 

 spermatogenesis, it was thought natural to describe some of the re- 

 sults which may prove important for the possible induction of poly- 

 ploidy in animals. This last problem will be discussed more 

 thoroughly in (Chapter 16. On the other hand, the disturbances of 

 embryonic growth related to mitotic poisoning result in some quite 

 peculiar malformations which will be considered later in this chapter. 



S.i-i: The cleavao^e of eggs. All work in this field points towards 

 the complexity of colchicine actions, which are not only related to 

 the stage of maturation or growth reached Ijy the eggs or the young 

 embryo, but also to the concentrations of alkaloid used. For instance, 

 in some of the early work on the egg of Rana pipiens the classification 

 of cellular changes proved to be very difficult because of great dif- 

 ferences of sensitivity. 1^ A 1:1000 solution suppressed all cleavage and 

 led to cellular disintegration; at 1:10,000, colchicine did not disturb 

 the first cleavage, but the next ones were irregular and the grooves 

 between the cells were only shallow; at 1:100,000, three cleavages 



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