126 



THE VOYAGE OF H3LS. CHALLENGER. 



In the line leading from the Protothaliate to the existing Doliolidae the muscle 

 bands have become distinctly circumscribed so as to form a definite number of com- 



d:t. n.f 



br.s. ^ si. 



V. af.vi. 



Fig. 15. — Diagram of the GonozooiJ of Loliolum, from the left side. 



at. atri.il aperture; at.h atrial lobes; ai.m. membrane lining peribranchial cavity; 6)'._ branchial apertme ; 

 br.l. branchial lobes ; hr.s. branchial sac ; d.t. dorsal tubercle ; end. endostyle ; h. heart ; /. intestine ; m. mantle ; 

 m' — ni^, muscle bands ; n. nerve ; n.g. nerve ganglion ; ov. ovary ; p.hr. peribranchial cavity ; i^.p. peripharyngeal 

 band; s.o. sense organs; s.gl. subncural gland; st. stomach; sg. stigmata; t. test; tes. testis; c. zona 

 pra^branchialis. 



plete circular bands surrounding the body like a series of hoops (Fig. 15). In all other 

 essential points the structure has remained unaltered. Anchinia^ I would place upon 

 a side branch from the base of the line leading to Doliolum (see table, p. 120). 



The line of ancestors leading to the Salpidte is longer, and a good deal more modifica- 

 tion has evidently taken place. The muscles in the mantle have become circumscribed 

 to form definite bands ; but these are irregularly placed, and in some cases are incom- 

 plete, while in others they branch. A well-developed but exceedingly clear and 

 gelatinous test has been formed, and the alimentary and reproductive viscera have 

 become concentrated (except in Cycloscdjxi) at the posterior end of the body to form 

 a rounded, opaque, highly-coloured mass, the so-called " nucleus " of the Salpa. The 

 branchial sac has undergone great modification — probably as the result of the rapid and 

 constant passage of streams of water through it — and at the present day its side walls, 

 where the stigmata were probably placed in the ancestral Protothaliate and still are in 

 some species of Doliolum (Fig. 15), have been converted into huge openings, leaving 

 merely the dorsal edge of the sac in the form of a vascular band (the dorsal lamina or 

 "gill") traversing the large open respiratory cavity (Fig. 16, cl.l.). All these changes 



^ For the structure of Anchinia and its close relationship to Doliolum, see Kowalevsky and Barrois, Journ. de 

 VAnat. et de la Physiol, torn. xix. 1883. Also Uljanin, Fauna und Flora des Golfes von Neapel, Monogr. x, Doliolum, 

 1884. 



