228 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



It is difficult to count accurately through the series of sections without 

 making a series of accurate drawings, and this is hardly worth while, as 

 a sufficiently close approximation can be made by counting, and the 

 number of nuclei is certainly not more than five hundred, and it is prob- 

 ably much less. 



As the peripheral nuclei give rise to the follicle and to the structures 

 which are derived from it, only a part of these five hundred can become 

 eggs ; but the number of eggs derived from the germinal mass during 

 the whole history of the stolon and its buds is very much greater than 

 five hundred, and the need for the multiplication of the embryonic germ 

 cells is clear. 



In fact, the persistence of a mass of embryonic, actively multiplying 

 cells at the base of the old stolon is in itself an indication that the number 

 of ova is at no time equal to the future demand. 



The context of Seeliger's paper shows clearly that his statement on 

 page 36, that " es lasst sich leicht feststellen, dass eine die spatere Eizahl 

 um ein Mehrfaches iibertreffende Anzahl von Zellen die ersten Umbild- 

 ungen erfahrt, welche zur Entstehung des Eies fahren," refers to the 

 very early stages of the genital string, although both this author and 

 Salensky (Pyrosoma, p. 78) appear to have been led to this view by the 

 fact that in Salpa democratica, the species which these authors have 

 investigated most exhaustively, the portion of the genital string which 

 passes into the body of the chain-salpa contains, in addition to the single 

 perfect egg, two or three others, which are small and abortive, and soon 

 disappear. In Salpa pinnata this is not the case, for each chain-salpa 

 receives only a single egg closely invested by its follicle, and I believe 

 that the abortive eggs of Salpa democratica are to be explained in another 

 way, as a reversion to a primitive condition of this species. Each chain- 

 salpa of Salpa hexagona and of Salpa cordiformis receives four or five 

 perfect eggs, as is shown in Plate XLV, Figs. 6 and 7. Salpa democratica 

 is certainly very close to Salpa cordiformis, and it is therefore probable 

 that its recent ancestors carried several eggs each, and produced several 

 embryos, like Salpa cordiformis; and the abortive eggs are therefore to 

 be regarded as eggs which underwent development in the cordiformis- 

 like ancestor. There seems to be some slight ground for the belief that 

 one or more of these abortive eggs of Salpa democratica may occasionally 

 complete their development and give rise to embryos after the manner 

 of Salpa cordiformis, for Salensky, " Neue Untersuchungen," p. 382, says 

 that he has found an egg in a chain-salpa of this species which had 

 already produced one embryo. 



