A STATISTICAL STUDY OF MITOSIS AND AMITOSIS. 



223 



an achromatic halo. In the lumen of the intestine are some 

 scattered yolk spheres derived from the macromeres and the 

 ingested food-ova. At one point, gv, is shown the fragment of 

 a germinal vesicle. 



When the larva has reached the distended condition of a fully- 

 gorged cannibal, the entoderm is very different from that shown 

 in Fig. 2 (see Fig. 2). At this time the entoderm has been 



exk 



''mm* 



Fig. 3. Part of a section through a fully gorged cannibal, cut in a plane passing 

 through one of the external kidneys [ex.k. ). Notice particularly the character of the 

 entoderm (ent. ) the cells of which are now spindle-shaped and provided with very 

 long and delicate processes. At m, two of the entoderm cells are dividing mitotically. 



so highly stretched that most of its earlier characteristics have 

 disappeared. In the first place the cells, except immediately 

 beneath the external kidneys, are so closely crowded against the 

 ectoderm that it is difficult to distinguish two membranes even in 

 those regions where in earlier stages ectoderm and entoderm were 

 separately and distinctly recognizable. The cells also are now 

 possessed of distinct boundaries, are spindle-shaped where clearly 

 visible and are connected by such long and finely attenuated 

 processes that one often finds hiatuses. The presence of these 

 breaks in the membrane lead Osborn ('04) to conclude that there 

 is at this time not enough entoderm to enclose the food-ova. 

 My own sections have convinced me that the hiatuses are due 

 not to the incompleteness of the membrane in which they occur, 

 but to its extreme delicacy. It is only preserved in exceptionally 

 good specimens, but these together with the condition exhibited 

 by the earlier larvae, seem to me to warrant the conclusion that 

 the entoderm is normally a complete membrane. The ectoderm 

 in these fully gorged cannibals has essentially the same cellular 

 character as the entoderm, and in perfect sections is complete. 



