W. K. BROOKS ON THE GENUS SALPA. 221 



Uljanin holds the same view, and says (7, p. 42) that the mass of 

 cells from which the eggs of doliolum, as well as the follicle around 

 them, are derived, must be regarded as corresponding to the germinal 

 epithelium of vertebrates. A few of the cells become eggs, as in the 

 elasmobranchs and other vertebrates, and these are nourished at the 

 expense of the other cells in their vicinity, a few of which give rise, 

 later on, to the follicle which surrounds the eggs. 



Seeliger, in his account of the origin of the eggs of clavelina (p. 6), 

 seems to hold the same view, and says that only a few of the cells which 

 make up the rudiment of the ovary become eggs, while the others are 

 arrested and turned to nutritive purposes, and that it may well be the 

 position of each cell in the young ovary and its relations to the sources of 

 nutrition which determine what its fate shall be. He speaks of the 

 arrested cells as sisters of those which become eggs, and in the case of 

 clavelina he clearly regards all the cells as homologous with each other, 

 and as potential eggs. 



Van Beneden and Julin (Rech. sur la morphologie des Tuniciers, 

 Arch. Biol., 1884, pp. 350-3) hold that the primordial ova and the cells 

 of the follicle are homologous structures, arising by divergent specializa- 

 tion in the germinal epithelium. 



Davidoff (16, p. 124) says that his study of the origin and nature of 

 the follicle cells in distaplia and clavelina has led him to results which 

 are in perfect accord with those of the last authors. It is hardly neces- 

 sary to state that, in other groups than the tunicates, the follicle cells are 

 almost universally regarded as germ cells which have been secondarily 

 set apart for other functions. 



In the section on the follicle I shall have occasion to refer to the 

 subject again, and to quote observations in other groups of the animal 

 kingdom, but those to which I have referred are enough to show that 

 prevailing opinion is on the side of Salensky as opposed to Seeliger; 

 and Salensky's view that the follicle cells are potentially germ cells, and 

 that their forerunners in the bodies of distant ancestors were actual 

 germ cells, seems to me the most logical position. 



SECTION 5. The Maturation of the Egg. 



In Plate XXXI, Figs. 4, 5, 6, 7 and 8, are given five sections through 

 the germinal mass, from a stolon a little older than the one shown in 

 Plate XXI, and in about the same stage as Plate XLI, Fig. (i. They are 



