530 CELL DIVISION IN EGGS OF CREPIDULA. 



VIII. Effects of Carbonic Acid. 

 (Plate LII. Exps. 1163-1169, 1169a, 1169b.) 



Carbonic acid was first employed by Delage (1902) to produce artificial par- 

 thenogenesis in starfish eggs, and it has since been employed by many other 

 investigators for this purpose. A cytological study of its effects on eggs has been 

 made by Godlewski (1908). Loeb (1906) and Godlewski (1908) found that 

 membrane formation in unfertilized echinoderm eggs could be called forth by this 

 substance. Godlewski observed that in C0 2 solutions parthenogenetic mitoses 

 are not preceded by nuclear growth, and that in strong C0 2 solutions fertilized 

 eggs rarely segment, though nuclei may continue to divide, thus giving rise to 

 cells with many nuclei. Later these nuclei may fuse together producing syn- 

 karyonts (Strasburger, 1907), which may subsequently divide by bipolar or multi- 

 polar mitoses; the size of the plasma field which subsequently cuts off around such 

 nuclei is proportional to the size of the nuclei. 



Only a few experiments were tried to learn the effects of carbonic acid on the 

 cleavage processes in Crepidula but they yielded some very interesting results, 

 and they call for an extension of these experiments. 



Normal sea water was charged with C0 2 in the well-known "sparklet siphon" 

 bottle, and equal parts of this charged sea water and normal sea water were 

 poured over the eggs in finger bowls, which were loosely covered. The eggs were 

 left in this water for from 7 to 42 hours, and were then fixed, stained, and mounted. 



A large number of the eggs so treated are abnormal and some of these abnor- 

 malities are highly characteristic. Among these may be mentioned the following : 

 All cell membranes appear unusually heavy and chromatic so that the outlines 

 of the cells are extraordinarily distinct, at the same time these membranes are 

 often wrinkled or separated from the cell substance (figs. 119, 130 memb.) 

 and on many of the cells there are lobes, bridges, and threads (figs. 127, 130, L). 

 comparable to those observed by Andrews (1898) in the so-called "spinning 

 phenomena." The cleavage of the yolk may be entirely or partially suppressed, 

 a phenomenon which is of frequent occurrence in many other experiments, while 

 the cleavage of the protoplasmic part of the egg goes on in more or less normal 

 manner. Thus in figs. 119-121, the cleavage of the yolk is entirely suppressed 

 but several "micromeres," some of them with several nuclei and spheres, have 

 been formed at the protoplasmic pole. In fig. 122, which has an abnormally 

 large second polar body, the first cleavage spindle has divided the nuclei in a 

 normal manner, but the cleavage furrow has cut down through the protoplasm 

 into the yolk and there stopped in a "cleavage head" (Ziegler, 1903), such as is 

 found in the cleavage of the eggs of many ccelenterates. In no other preparations 

 of Crepidula eggs have I found such a type of cleavage as this and it would be 

 interesting to learn whether this ccelenterate type could be produced in other 

 eggs by the use of C0 2 . The area marked S in the yolk of fig. 122 may be a 

 sphere or "cy taster." 



