kofoid: development of limax. 41 



a small protoplasmic mass budded off from a larger mass. This concep- 

 tion of the cell division — the derivation of a small part from a large 

 part — dominated Blochmann's nomenclature both of cells and of spirals. 

 Accordingly, we find him designating a large mass of protoplasm, both 

 before and after the small mass is budded off from it, by the same name. 

 So also, when he comes to compare the spiral with the motion of the 

 hands of a clock, he regai"ds the small cell as moving away from the large 

 cell, and designates the spiral accordingly. Other investigators of spiral 

 cleavage — Lang ('85), Conklin ('91 and '92), Wilson ('92), Heymons 

 ('93), Lillie ('93) — have, like lilochmann, dealt with forms presenting a 

 greater or a less inequality in cleavage, and have found it convenient to 

 employ the system inaugurated by Blochmann for their nomenclature 

 of cells and spirals. There has ai'isen in the usages of these various 

 authors, however, considerable confusion in the detailed application of 

 their nomenclatures to this basis of reference. Indeed, as I have pointed 

 out in a previous paper (Kofoid, '94), an author is not always able to 

 avoid inconsistencies. This state of affairs is confusing and extremely 

 annoying to the student who wishes to make a comparative study of 

 cell lineage. However much the introduction of a new system of nomen- 

 clature is to be deplored, it seems to be justified for the following reasons. 

 Cell lineage deals primarily with the descent and fate of cells, and is most 

 conveniently traced by following the history of their nuclei ; it is only 

 secondarily concerned with the amount of yolk or protoplasm in the 

 cells. The founding of a system of nomenclature, therefore, upon the 

 relative sizes of cells, ignores wholly this fundamental proposition, and 

 substitutes a basis of varying and uncertain natui'e. Fui-thermore, this 

 system has caused the introduction, perhaps not necessarily, . of the 

 custom of designating cells of different generations by identical names ; 

 thus A may be a cell of any one of a half-dozen different generations. 

 In this, too, the principle of descent is ignored. 



Finally and principally, the basis hitherto employed affords no solid 

 ground whatever for comparisons^ for it gives no logical method to be 

 employed in cases of equal cleavage ; and its application must vary with 

 the varying distribution of the large cells in different species of animals. 

 Thus it comes about that " homologous" cells, i. e. those of identical 

 descent, must according to this system be named differently in differ- 

 ent animals. It may be that the system as applied by these authors 

 does furnish a means, readily gi-asped by the eye and the mind, of fol- 

 lowing the lineage in the particular form studied ; but so long as it fails 

 to form a basis for comparison, it is open to serious objection. It was 



