REPORT ON THE TUNICATA. 



'.).) 



observations on various species of Salpa, and most writers on the Tunicata have 

 discussed the position and affinities of this alierrant genus ; but the most important 

 memoirs since I860 have been confined to the embryology, the gemmation, and the lifc- 

 liistory. Amongst them may be mentioned especially the works of Salensky, Todaro, 

 Brooks, and Seeliger. Of these the most important are the researches of Salensky,' to 

 which we owe the greater part of our detailed present knowledge of the embryology of 

 Salpa. The accounts given by Todaro" conflict in many points with the descriptions by 

 other authors ; and Brooks'' has put forth the remarkable view that Salpa is not after 

 all an example of alternation of generations, but that the ovary really belongs to the 

 solitary form, which is therefore a female producing a series of males (the aggregated 

 forms) by asexual gemmation and depositing in each of them an ovum which will after- 

 wards, when fertilised, develop in the body of the male into a solitary or female Salpa. 

 Thus, according to Brooks, the female produces two forms of young — males asexually, 

 and females sexually ; and these two foi-ms differ not only in mode of origin and sex, 

 but also in structure. There are, however, no sufficient grounds for supposing that the 

 ovum does not belong to the Saljja in which it develops, and therefore the sexual or 

 chain form is usually regarded as a protogynous hermaphrodite, producing first an 

 ovum, which is fertilised by the spermatozoa of an older Salpa of the same kind, and 

 then, after it has got rid of the embryo, developing a testis. The embryo, on the other 

 hand, becomes a solitary Salpa which is asexual, and produces the aggregated forms !)}• 

 gemmation. 



The structure of the adult (sexual) Salpa is shown in Fig. 7. 



br.m. '.■' "''• 



I \ m; \ s,y.Z. ; n' 



k. 



Z.'" 



at 



atvL 



i; 



oe. k 



Fig. 7. — Semi-tliagrammatic reijreseutation of Salpa from the left side. 

 11. anus ; at. atrial aperture ; nt.iii. muscles of atrial aperture ; br. branchial aperture ; lir.m. muscles of branchial 

 aperture; br.s. branchial sac; d.l. dorsal lamina ( = "giH"); d.t. dorsal tubercle; ijtcl. endostyle ; h. heart; 

 i. intestine ; l. languet ; m. mantle ; m' — m'". muscle bands ; n.g. nerve ganglion ; o. tesopliagus ; w. embryo in 

 ovisac; p.bi: peribranchial cavity; jj.}}. peripharyngeal Ijand ; st. stomach; s.yl. subneural gland; t. test; 

 t'. thickened test over viscera ; tes. testis ; ,:. zona priebranchialis. 



' Zeitsclir.f. icisg. ZouL, Bd. xxvii. xxviii. xxx. &c. 



- Alt! (hUa U. Accud. iki L'mcci, 187,i, 188;), 1887, &c. 



= Bull. i\[»s. Comp. ZviiL, vol. iii. No. 14, p. 291, 1876. 



