566 MAYNARD M. METCALF, 



issue with Salensky as to the ultimate fate of blastomeres and follicle, 

 claiming and clearly showing that in the later stages the follicle cells 

 composing the rudiments of the organs are replaced by true blastomeres 

 which give rise to the adult. He says p. 27 : "Stated in a word, the 

 most remarkable peculiarity of the Salpa embryo is this. It is blocked 

 out in follicle cells which form layers and undergo foldings and other 

 changes which result in an outline or model of all the general features 

 in the organization of the embryo. While this process is going on 

 the development of the blastomeres is retarded, so that they are 

 carried into their final position in the embryo while still in a very 

 rudimentary condition. Finally when they have reached the places 

 they are to occupy, they undergo rapid multiplication and growth, 

 and build up the tissues of the body directly while the scaffolding of 

 follicle cells is torn down and used up as food for the true embryonic 

 cells." 



Brooks' figs. 1 and 2, tab. 62, also fig. 12, tab. 9, as well as 

 his descriptions, demonstrate that the peculiar granular bodies seen 

 within the blastomeres at certain stages of development are not an 

 indication of the fragmentation or degeneration of the blastomeres, 

 but are nuclei of follicle cells that have been ingested and are 

 undergoing digestion. This statement I have fully confirmed, as de- 

 scribed a few pages beyond. The amitotic division of the migrating 

 follicle cells confirms the belief that they are on the road to degener- 

 ation, and in the centre of the embryo there are found masses of 

 such disintegrating cells. 



Heider's account of the embryology of Salpa fusifarmis, pub- 

 lished in 1895, differs in certain points from preceding accounts. 



He interprets the granular bodies in the protoplasm of the blasto- 

 meres as ingested follicle cells and figures them as containing 

 nuclei (tab. 1, figs. 4, 10a, 10b), and largely from this observation 

 argues, as Brooks had shown, that the follicle cells serve as food 

 for the blastomeres. 



Heider places emphasis upon the unequal cleavage of the SaljM 

 ovum, claiming, contrary to Salensky and Brooks, that, except in 

 the early stages, the micromeres can not be distinguished from the 

 follicle cells, and that organ rudiments which are apparently formed 

 from follicle cells are really composed of small blastomeres. 



The insufficient reference in Heider's paper to Brooks' Mono- 

 graph may perhaps be explained by the fact that Heider's paper was 

 practically complete before Brooks' work was published. 



