REPORT ON THE TUNICATA. 



59 



Out of the enormous number of aggregated Salj}<v collected during the Challenger 

 Expedition, none were adhering together when they reached my hands. In all cases 

 the chains, being fully develojaed, had become broken up into their constituent Salj^ie. 



Each species of Salpa thus occurs in two very distinct forms (Fig. 9, A and B), — 

 the solitary asexual (proles solitaria) and the aggregated sexual {proles yregata, or 

 " chain "), — and the latter may either be found united together in a chain or singly (see 

 fig. 9, B). 



end-- 



Fig. O.—Salpu runcinata-fiisiforiiiis. A. Solitary form. B. Aggregated form.— (From the Encyclop.^dia Britannica, 9th ed.) 

 1-9. muscle bands; at. atrial aperture; Ir. branchial .aperture; d.l. dorsal lamina; d.t. dorsal tubercle; 

 cm. embryo ; e/id. endostyle ; acm. gemmiparous stolon; m. mantle; n.(/. nerve ganglion ; pp. peripharyngeal band ; 

 vise, visceral mass (nucleus). 



This circumstance, and the fact that both forms of most species had been found and 

 described before their relationship to one another was discovered, has led to the applica- 

 tion of two specific names to each species — not as synonyms, but the one applicable to 

 the solitary form and the other to the aggregated. Thus in the case of the species 

 represented in fig. 9, the solitary form is generally known as Sal2xc runcmata, 

 Chamisso, and the aggregated form as Salpa fusiformis, Cuvier ; and it has become 

 customary when writing of the species as a whole to use both names and both 

 authorities ; thus — Salpa runcinata-fusiformis, Chamisso-Cuvier. This plan was first 

 employed by Krohn in 1846 ;^ it was adopted by Trau.stedt in his admirable revision 

 of the species of Saljja published in 1885, and I have followed it here. 



If, on the other hand, one of the names were to be chosen to indicate each species 

 of Salpa, then two alternatives would be open: (l) To follow priority only, without 

 reference to the sexual condition of the form first named ; and (2) to choose in all cases 

 the earliest name of the sexually mature or chain form of the species. Tliis second 

 course, which seems in some respects the preferable one, would result in a form being 

 chosen to give its name to the species which is not larger, nor more highly organised, 

 nor longer lived than the other form, but merely because it reproduces sexually. And, 



' Ann. d. Sci. Nat. (Zool.), ser. 3, torn. vi. p. 110. 



