TUNICATA. 



1231 



around the tube. The last two sent! lateral 

 processes backwards, forming, with the suc- 

 ceeding band, the first on the trunk, and also 

 annular, large rhomboidal meshes ; two other 

 annular bands succeed and form large meshes 

 by intercommunications on the upper and 

 lower surfaces. From these last muscles two 

 intercommunicating processes are sent off on 

 each side to the crestlike prominence of the 

 test. From the last band several branches 

 run backwards to be distributed to the upper 

 and lower lips of the posterior orifices. 



In S. Tilesii the anterior orifice is provided 

 with two lateral penniform muscles. The 

 other muscles form six bands nearly parallel 

 with each other, interrupted along the me- 

 dian line of the superior surface, and not 

 reaching further than halfway down the sides 

 of the body. The most anterior band is 

 somewhat forked, and the most posterior 

 gives some branches to the superior lip of the 

 posterior orifice, and joins, at the an>le of the 

 lips, a radiating group of other fascicles, that 

 are distributed to the inferior lip. 



In S. scutigera the muscular bands are few. 

 On the superior surface, two pairs of decus- 

 sating muscles are seen, and other smaller 

 bands occur near the extremities. In S. cy- 

 lindnca there are eleven transverse bands, 

 interrupted and separated by a considerable 

 space on the inferior surface of the body ; the 

 first six of which are parallel one to another, 

 whilst the four following are bent towards 

 each other on the median line of the body ; 

 the last band, and some short lateral fascicles, 

 are arranged close by the posterior ex- 

 tremity. In S. fusiformis there are seven 

 transverse bands ; some of which are parallel 

 with, and approaching others on the sides of 

 the animal, and others are more or less 

 obliquely arranged. In S. cordiformis there are 

 six broad transverse muscles on each side of 

 the animal, not meeting on either surface. 

 Two narrow, looplike fascicles, one above and 

 one below, arising from the last branchial 

 bands, and two short, transverse, lateral slips, 

 act as sphincters to the posterior orifice. 

 A pair of narrow muscular fascicles are 

 sent off from the first of the branchial muscles 

 to the anterior orifice. In S. zonaria (the 

 aggregate form or "proles" of S. cordiformis) 

 there are also six transverse bands interrupted 

 only on one surface, and differing consider- 

 ably from those of S. cordiformis, as do the 

 distinct sets of muscles distributed to the two 

 orifices. In S.runcinata (solitary) ( _fig.772. A) 

 the muscular bands are nine in number, placed 

 on the dorsal surface ; three anterior and 

 three posterior, approximated at their centres, 

 and three parallel bands in the middle. In 

 S. runcinata (aggregate) (Jtg.772.ii) there are 

 six muscles, besides those of the orifices ; four 

 anterior and two posterior, approximating on 

 the median lines. 



The bronchia is single, in the form of a 

 riband-like tube, stretched, on a vertical plane, 

 obliquely across the central or branchial cavity 

 of the body, so that it is constantly bathed by 

 the water traversing this cavity. It consists 



of a double membrane formed by a fold of the 

 internal tunic or mantle, and springs anteriorly 

 from the visceral nucleus between the ceso- 

 phageal opening and the orifice of the rectum ; 

 it then becomes free, and ultimately terminates 

 on the superior part of the thoracic cavity, 

 below the point where the nerve-ganglion and 

 the oculiform organ are found. It thus di- 

 vides the branchial cavity into two portions 

 the antero-dorsal or pharyngeal, and the 

 postero-ventral or cloacal. 



The inferior border of the branchia exhibits 

 an infinite number of minute transverse ves- 

 sels, all parallel to each other. There is 

 usually only a single row of these transverse 

 vessels on each side of the foliole of the bran- 

 chia ; but sometimes there are many rows, 

 which indicate the presence of many longi- 

 tudinal vessels, and thereby approach the 

 character of the branchial tissue of the As- 

 cidians. 



Savigny observed in S. octofora another 

 small branchia near the anterior insertion of 

 the large branchia. 



The whole inner surface of the branchial sac 

 of the Salpae seems, from its high degree of 

 vascularity, to be subservient to the purposes 

 of respiration. The vascular tissue of the bran- 

 chia, consisting of longitudinal and transverse 

 vessels, is equivalent to the x vertical bran- 

 chial network dividing transversely the respi- 

 ratory cavity of the ClaveUince. 



The single branchial lamina of Salpcc ap- 

 pears to constitute the transition from the 

 Ascidice to the Teredines; in the latter there 

 are two elongated branchial laminae above the 

 intestine, and within the tubular mantle, to 

 which the water has access and egress by 

 means of two tubes placed at the posterioi 

 extremity of the body. 



The intestinal canal is opaque, fuscous, 

 or variously tinted, generally closely folded 

 or convolute, and sometimes enveloped in 

 the liver, forming altogether the " visceral 

 nucleus." This, together with the heart, lies 

 external to the mantle, between it and the 

 test. The cesophageal aperture is in the 

 antero-inferior part of the body, behind the 

 heart, more or less conspicuous and variously 

 modified ; dissimilar in the alternate " proles " 

 of the same species. In the solitary " proles" 

 of S. pinnata and S. affinis it is stretched 

 above the branchia. In the aggregate " pro- 

 les " of S. pinnata it is opened out longwise, 

 and of a violet colour in the living specimen. 



In <S". cristata the intestinal canal has the 

 following characters. The oesophagus is 

 round, with a loosely plicated margin ; the sto- 

 mach has a contrary direction to the rest of 

 the canal, being a cul-de-sac pointing ante- 

 riorly, and situated in the thickness of the 

 antero-inferior protuberance of the test. It 

 is membranous and transparent, and is de- 

 scribed by Cuvier as ordinarily containing a 

 little greyish fluid. The intestine is a simple 

 tube having a direction unusual among the 

 Salpians ; it runs from the stomach towards 

 the posterior extremity of the body, where it 

 opens into the branchial cavity by a rather 



