Experimental Studies on Germinal Localization. 31 



Crampton ('96) in his interesting paper on Ilyanasssa, found 

 that after removal of the polar lobe the second somatoblast (4d) 

 differs from the normal not only in being no larger than the 

 other members of the quartet, but also in texture, being filled 

 with yolk-spheres instead of being mainly composed of clear 

 protoplasm as in the normal, and it also lies at first at the sur- 

 face, exactly like 4a, 4b and 4c. This observation I can confirm 

 from a reexamination of the original preparations, kindly placed 

 at my disposition for this purpose by Dr. Crampton. He found 

 further, that the larvae produced from such eggs lacked the 

 mesoblast-bands present in the normal larva, 4d apparently enter- 

 ing, like its fellow-members of the same quartet, into the forma- 

 tion of the archenteron. 



This highly interesting result, which has atracted considerable 

 attention, was based on the examination of total preparations 

 only; and the desirability of a more adequate study of the matter 

 by means of sections has long been obvious. I have accordingly 

 given especial attention to this point as far as my material would 

 allow; but must admit that neither in point of abundance nor 

 of fixation is this material quite adequate for the full investigation 

 of the question, which indeed would demand a complete study of 

 the cell-lineage, both in the normal and in the lobeless forms. 

 Nevertheless such evidence as I hav^e obtained is distinctly in 

 favor of the correctness of Crampton's result. 



The mesoblast may be most clearly seen in the normal larvae 

 in cross sections through the region of the prototroch, where the 

 gut shows two chambers and the complication produced further 

 back by the shell-gland and mantle-folds are not present. In such 

 a section (Fig. 38) the gut appears in the form of two distinct 

 chambers, the wall of the ventral one being a little further back 

 intimately connected with the stomodaeal invagination (Fig. 39') 

 though its cavity does not yet appear to communicate with the 

 outside. The walls of both chambers are composed of large 

 cells, more or less columnar and radially disposed, completely 

 filled with yolk-spheres (as are all the cells at this time) and with 

 large nuclei. On either side is a loose group of much smaller 

 cells with small nuclei, that appear irregular or often spindle- 



