W. K. BROOKS ON THE GENUS SALPA. 231 



In support of this view I appeal to Seeliger's own figures (11), and I 

 will ask the reader to examine the following representations of the egg 

 of salpa: Taf. IX, Fig. 5; Taf. VIII, Figs. 2, 3, 4; Taf. VII, Figs. 14, 11, 3, 

 2, 1; Taf. VI; Taf. V; Taf. IV, and Taf. Ill, Figs. 14, 12 and 11. 



It is true that the eggs continue to grow and to ripen as the stolon 

 develops, but no new ones are formed anywhere except in the embryonic 

 germinal mass, and as this is recognizable in the body of the embryo, 

 page 208, before the stolon is formed, it is plain that the eggs are older, 

 as independent definite cells, than the chain-salpae, and I have shown, 

 page 19, that in those species which produce four or five embryos, four or 

 five eggs pass into the body of each chain-salpa. 



When in arthropods, cestodes, molluscs or echinoderms, the ripen- 

 ing place of the eggs is different from their place of origin as definite 

 cells, this latter spot is universally regarded as the ovary, and if the 

 bodies which are shown in my Plate XXXII, Fig. 7, are eggs, so also are 

 those shown in Plate XXVI, Plate XXIII, Plate XV, Plate XXXIV and 

 Plate XLI, Fig. 9; while the place where the central cells of the germinal 

 mass are found in a state of vegetative activity, Plate XLI, Figs. 8 and 7, 

 is the true ovary. 



A third criticism of my view now remains to be noticed. 



Weismann (Die Entstehung die Sexualzellen bei den Hydromedusen, 

 Jena, 1883) says, p. 294, that the view that the development of salpa is 

 an alternation of sexual and asexual generations, can only be set aside 

 when it is shown that the egg cells which are contained in the stolon 

 belonged, at an earlier phyletic period, to the nurse itself ; that they were 

 formerly the cells of the ovary of the solitary salpa, and that they have 

 in the course of evolution been pushed out into the bodies of the chain- 

 salpae. 



I hold that there is evidence that the eggs which are fertilized in the 

 chain-salpae are phylogenetically the eggs of the solitary salpa. 



Each zooid of pyrosoma produces buds, and these buds in their turn 

 produce buds, and so on indefinitely. Each of them has a testis and an 

 ovary of its own, derived from the germinal rudiment of the preceding 

 generation, and each of them has an egg, which is fertilized and under- 

 goes development in its body. Each of them also produces an egg, but 

 this passes over into a new bud, with the rudiment of the ovary and 

 testis, to mature and ripen there and to be fertilized. 



Recent writers on salpa speak of the single egg of the chain-salpa as 

 an " ovary," but as each pyrosoma has an ovary of its own capable of 



