W. K. BROOKS ON THE GENUS SALPA. 19 



1, m, and to the fertilizing duct, x, by which the egg is attached to the 

 wall of the cloaca of the chain-salpa, as shown in Fig. 10. The thickened 

 layer of epithelium gives rise .to the testes. 



As the constrictions which mark out the bodies of the chain-salpae 

 make their appearance in the walls of the stolon, the germinal mass also 

 becomes divided up, Plate XV, Figs. 1 and 2, and Plate XXIII, Figs. 1, 2 

 and 5, into a series of segments, one for each chain-salpa. In Salpa pin- 

 nata, and in most species, each of these segments contains a single egg ; 

 but in those species which produce several embryos, such as Salpa cordi- 

 formis and Salpa hexagona. the number of eggs is the same as the num- 

 ber of embryos which is characteristic of the species. Thus the chain 

 form of Salpa hexagona, Plate III, Fig. 1, normally gives birth to five 

 embryos, and as shown in Plate XLV, Figs. 6 and 7, each segment of the 

 genital string contains five eggs. Salpa democratica appears to be in an 

 intermediate condition, for while it normally produces only one embryo, 

 the segments of its genital string often contain, in addition to the single 

 normal egg, one or two others which appear to be abortive, and which 

 often exhibit indications of degeneration, although Salensky thinks there 

 is reason to believe that a second embryo may be produced in this species 

 after the first one has completed its development and has been set free. 



As the body cavities of the chain-salp* become separated from each 

 other, the thickened epithelium under the egg becomes folded and pushed 

 out to form two lateral pouches, Plate XV, Fig. 1, m, and Plate XXIII, 

 Figs. 1 and 2, m, which are to give rise to the testes ; and at a somewhat 

 later stage a third fold or outgrowth appears on the middle line and 

 ultimately becomes the fertilizing duct. This outgrowth, which is indi- 

 cated in Plate XXV, Fig. 7, H, by the letter m, is derived from the 

 epithelium of the follicle on the dorsal or neural side of the egg. In Plate 

 XXV, Fig. 7, (7, all three folds, the two paired testicular folds, and the 

 unpaired median fold which represents the fertilizing duct, are shown, 

 colored blue; and they are also shown in Plate XXVI, Fig. 1, .ff and G, 

 and Figs. 2, E and F. 



As the bodies of the chain-salpse become developed and undergo 

 changes of position, the reproductive organs also move away from their 

 primitive positions, in a manner which will be readily understood from 

 the figures. At the stage shown in Plate XXXIV, Fig. 4, the ovary is a 

 continuous structure in a continuous sheath of follicle cells. At the stage 

 shown in Plate XV, Figs. 1 and 2, and also in the reconstruction in Plate 

 V, Fig. 1, the testicular folds, m, have appeared, and the follicle is con- 



