W. K. BROOKS ON THE GENUS SALPA. 261 



Crinoiden, Jenaische Zeitschr. XXXII, p. 278) that in the ophiurans the 

 egg cell is surrounded by flattened follicle cells, which are, in origin, 

 germ cells which have not developed into eggs. They are often found 

 breaking down, and their cell substance thus affords the nutritive 

 material for the growing eggs. 



It is not necessary to give more quotations, for these are enough to 

 show that there is abundant analogy for my interpretation. 



The Migration of the Follicle. 



The nutritive function of the follicle cells, which is established at 

 this early stage in the history of the salpa egg, becomes very important 

 after the egg is fertilized; and the migration of the follicle cells into 

 the embryo, which is now to be described, is certainly one of the most 

 remarkable phenomena in the life-history of salpa. Todarro seems to 

 have observed it, but its importance as a dominant factor in the embry- 

 ology of salpa was first recognized by Salensky, who has made a minute 

 study of the subject, and has discussed it, at great length, in his memoir 

 on the embryology of salpa (5), and more recently in his paper on the 

 embryology of pyrosoma (17). The discovery of the remarkable history 

 of the follicle cells is one of the most important steps towards a thorough 

 comprehension of the life-history of salpa, and, in itself, it is enough to 

 give to Salensky's memoir a most prominent place in the literature of 

 the subject, although my own observations, while confirming his account 

 of their origin, have forced me to differ from him regarding a most 

 essential and fundamental feature, the fate of these cells. 



I regard the cells which migrate into the embryo as exclusively 

 nutritive, like those which migrate into the egg, while it is well known 

 that Salensky holds that they become incorporated in the tissues of 

 the embryo. 



At the end of this section I shall state and discuss his views, but at 

 present I shall confine myself to the presentation of my own observa- 

 tions. 



In a ripe unfertilized egg, Plate X, Fig. 1, the follicle, which is 

 colored blue in the figures, is one cell thick, and over most of the 

 surface of the egg the cells are nearly cubical, although they become 

 larger as they approach the region of the duct, x. Their nuclei are sub- 

 spherical, with a fine network of chromatin. Here and there, in the 

 sections, a cell is found in process of division, but cell multiplication is 



