Ill 



SALPA — STRUCTURE 



105 



most cases a retina formed of elongated cells, and a pigment-layer 

 placed upon the ganglion. 



The so-called otocysts of Salpa have been shown by Metcalf 

 to be really glandular organs. They have been called lateral 

 neural glands ; they do not open at the dorsal tubercle, but 

 separately into the pharynx. These lateral neural tubular glands 

 have also been regarded as nephridia. 



The large spaces at the sides of the dorsal lamina (often 



s.gl THUS, ids 



o^-: ^^ .-.■-. 



brn 



dt 



Fig. 65. — Diagrammatic sagittal section of a " chain " Salpa. an. Anus ; at, atrial 

 aperture ; at.m, muscles of atrial aperture ; atr. cav, atrial cavity ; br, branchial 

 aperture ; br.m, muscles of branchial aperture ; itr.s, branchial sac ; d. I, dorsal 

 lamina or "gill " ; d.t, dorsal tubercle ; end, endostyle ; fit, heart ; int, intestine ; 

 I, sensory languet ; mus.hds, muscle-bands ; n.g, nerve-gangliou ; oc, eye-spot ; oe, 

 oesophagus ; ov, ovary ; p.p.b, peripharyngeal band ; s.gl, neural gland ; stom, 

 stomach ; t,t', test ; tes, testis ; a, prebranchial zone. (After Herdman.) 



called the gill or branchia of Salpa), by means of which the 

 cavity of the branchial sac is placed in free communication with 

 the peribranchial cavity, are to be regarded as gigantic gill-slits 

 formed by the suppression of the lateral walls and small stigmata 

 of the branchial sac. The alimentary canal at the posterior end 

 of the " gill " consists of oesophagus, stomach, and intestine, with 

 a pair of lateral gastric glands or caeca. These viscera along 

 with the reproductive organs, when present, make up the 

 "nucleus" (Fig. 66, v). 



Alternation of Generations. — Fig. 66 represents an 

 aggregated or sexual Salpa, which was once a member of a chain, 

 since it shows a testis and a developing embryo. The ova 

 (always few in number, usually only one) appear at a very early 

 period in the developing chain Salpa, while it is still a part of 

 the gemmiparous stolon in the body of the solitary Salpa. This 

 gave rise to the view put forward first by Brooks that the ovary 



