1232 



TUNICATA. 



large anus. The faecal matter contained in 

 it is greenish and vermiform. The liver (testicle, 

 Krohn) in this species appears to be composed 

 of large, parallel, longitudinal filaments, and 

 terminates posteriorly in a delicate, tapering 

 point. It differs also from the liver of other 

 species in being of a whitish colour. 



The intestine of the Salpians is usually 

 twisted once or twice either around or within 

 the liver, with the anus terminating nearly free 

 of the latter, near the anterior attachment of 

 the branchia. The anus is generally on the 

 left side, opening posteriorly. The rectum 

 never traverses the heart. In S. gibbosa and 

 S. infundibuliformis the intestine makes a little 

 more than one turn, the two ends crossing 

 one another a little. It has two coeca, one on 

 each side, which are turned into the centre of 

 the loop of the intestine. Eschricht describes 

 the liver of S. zonaria as conspicuous, enve- 

 loping nearly all the alimentary canal, and 

 consisting of a mass of coecal tubes, each of 

 which bear, near their free extremities and on 

 one side only, a group of 2 6 minute, short 

 coecal appendages. 



The heart is with difficulty observed in 

 dead specimens, but, from its pulsating move- 

 ments, is generally conspicuous in the living 

 animals ; and in these only can the circulatory 

 apparatus be traced out. It is situated in the 

 antero-inferior region of the body, near the 

 visceral nucleus, the anterior attachment of 

 the branchia, and the generative organs. It 

 is a somewhat long, pellucid, tubuliform ve- 

 sicle, enclosed in an immoveable pericardium. 

 A longitudinal vessel or sinus (aorta, of Van 

 Hasselt) traverses the inferior surface of the 

 branchial cavity, and is continued into the in- 

 ferior lip of the posterior orifice, and into the 

 base of the posterior prolongation (if present) 

 of the test. Hence it is retroflexed and recur- 

 rent. It gives off numerous branches at right 

 angles on either side (fig. 787.) from which arise 



Fig. 787. 



Salpa maxima; showing the viscera and large vessels. 

 The fine vascular net-work of the branchial sac is 

 not introduced. (After Milne-Edwards.) 



a, upper lip of posterior orifice ; Z>, anterior orifice ; 

 c, abdomen, containing the visceral nucleus ; d, bran- 

 chial lamina ; e, heart;/, oculifonn point; g, g, pro- 

 longations of the test, by which the animal is ad- 

 herent to its neighbours. 



a great number of smaller branches, that sub- 

 divide, anastomose, and spread out in different 

 parts of the body, forming a fine vascular net- 

 work. All the transverse canals open into a 

 large dorsal vessel, which thus receives all 

 the blood which has passed through the 



vessels of the branchial sac ; but, besides this, 

 some blood is also received by it, which has 

 not passed through this tissue, in consequence 

 of the great dorsal vessel being connected at 

 each extremity with the great thoracic or 

 abdominal vessel by two considerable annular 

 vessels. The blood returns downwards from 

 the dorsal vessel through a canal lying on 

 the dorsal surface of the abdomen (dorsal 

 canal) to the opposite end of the heart. The 

 vascular net-work is very conspicuous in S. 

 aspcra, and is sometimes particularly distinct 

 in the appendages. These ramifications go 

 off from one another at right angles, and 

 afterwards are, for the most part, bent back 

 archwise, as Chamisso and Van Hasselt have 

 observed ; so that, with the exception of 

 those running transversely, all these little 

 vessels have a direction contrary to that of 

 the principal vessels ; that is to say, they 

 are directed from behind forwards, whilst the 

 aorta runs from before backwards. At the 

 anterior extremity of the heart are two ves- 

 sels, that answer to the pulmonary veins 

 (dorsal sinus). They are equally distributed 

 in the body of the animal, anastomosing with 

 the branches of the principal sinus (aorta). 

 The circulation of the blood among the vis- 

 cera is carried on by means of variable in- 

 terspaces occurring between these organs. 

 The motions of the heart are made spirally, by 

 a twisting of its parietes, and always begin from 

 one or other of its extremities. As in other 

 Tunicata, this action is oscillatory, having an 

 alternately contrary direction, first impelling 

 the blood in one direction, then stopping, 

 contracting again, and soon impelling it in 

 an opposite direction ; so that, after the blood 

 has been flowing for some time from the heart 

 to the aorta, to be distributed to the body, 

 it stops, and then begins to run by the ar- 

 teries and the aorta to the heart, and from 

 thence, by the pulmonary veins and their anas- 

 tomoses, it returns into the arteries and aorta. 

 The contractions of the heart, in general 

 very regular, diminish in rapidity at the ap- 

 proach of the periodic change in the circu- 

 lation, the blood stopping, and even retreat- 

 ing a little until a general contraction of the 

 body determines it to take an opposite 

 direction. The duration of the opposite cir- 

 culation is not always the same. Van Has- 

 selt saw the blood flow for three-fourths of a 

 minute from the heart to the aorta ; and, dur- 

 ing this time he observed forty-two contrac- 

 tions of the heart ; and he saw it reflow from 

 the arteries to the heart and the pulmonary 

 veins for a third of a minute, and in this inter- 

 val he counted sixty-two pulsations. 



The motion of the blood is the more per- 

 ceptible as it is full of minute white globules, 

 which pass through the minute vessels in a sin- 

 gle row, and are easily seen through the trans- 

 parent parietes. These observations may be still 

 more assisted by holding the animal vertically, 

 with the nucleus downwards ; when, as the 

 blood, driven into the ventral sinus, is forced to 

 ascend against its own weight, its current is less 



