226 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



and as the eggs grow, they stretch out into a series which, in Salpa 

 pinnata and Salpa cylindrica at least, ultimately become a single row. 

 As the bodies of the chain-salpse are formed, eggs from this row are 

 folded off and pass into their bodies; one egg for each chain-salpa in 

 Salpa pinnata, Salpa cylindrica, and in most species, but five for each in 

 Salpa hexagona, where each chain-salpa gives birth to five embryos. 

 Salpa cordiformis probably resembles Salpa hexagona in this, and Salpa 

 democratica seems to be in a transitional stage, for while this species 

 usually gives birth to only one embryo, it seems to receive occasionally 

 more than one egg, the extra ones degenerating. 



The peripheral cells of the germinal mass form an epithelium around 

 the central core of eggs, and this epithelium retains its vegetative power 

 and grows throughout the whole length of the stolon by cell multiplica- 

 tion. As the eggs increase in size they are nourished by cells which 

 migrate from the epithelium in among the eggs and there degenerate. 



As the string of eggs lengthens the epithelium also lengthens, and it 

 ultimately forms a follicular capsule around each egg, or, in Salpa hexa- 

 gona, around each group of eggs, so that when the eggs pass into the 

 bodies of the chain -salpae they are enclosed in epithelial capsules or 

 follicles. After it has passed into the body of the chain-salpa the epi- 

 thelium gives rise to the testis and the fertilizing duct, but as a knowl- 

 edge of the history of these structures is not needed for our purpose, 

 the description of them may be left for the chapter on the development 

 of the chain-salpa3. 



The only derivative of the epithelium which concerns us here is the 

 follicle. As shown in Plate X, Fig. 1, the ripe egg is enclosed in a follicle 

 which consists of a single layer of cubical cells, with their central ends 

 in contact with the surface of the yolk and their outer ends bounded 

 by a basement membrane. 



SECTION 7. The Number of Eggs. 



Seeliger says, page 36, that it is easy to satisfy one's self that the 

 number of cells which pass through the first stages in the process of 

 modification which leads to the formation of eggs is very much greater 

 than the final number of eggs. He therefore believes that many of these 

 ovarian eggs are destined to become abortive, and, by degeneration, to 

 supply a part of the nutriment for those eggs which attain maturity. 

 He gives no numerical data as a basis for this impression regarding the 



