■68 Descriptions of Preparations. 



'branchiaP or Morsal sinus' of Milne-Edwards, the 'branchial 

 vein' of Savig-ny. It is connected with the one already spoken 

 of as holding a similar relation to the endostyle on the opposite 

 side of the branchial sac, firstly, by means of the numerous trans- 

 verse vessels encircling- the branchial sac ; secondly, by a vessel 

 taking a similar course to these vessels around a zone in relation 

 with the ' anterior collar •/ and thirdly, by a vessel holding a 

 similar relation to a chord uniting the upper end of the endostyle 

 to that of the oral lamina, and known as the ' posterior collar/ 

 The ' dorsal sinus ' receives factors from the pallial plexuses by 

 means of tubular ties similar to those which pass from these and 

 the visceral plexuses on the left side of the animal's body to the 

 other portions of the branchial network. Finally, it is seen to 

 receive a large vessel from the neighbourhood of the anus, and 

 by this vessel, which passes to it through the visceral mass from 

 the heart, it is brought into direct communication with the dorsal 

 end of that vasiform organ as the ' thoracic sinus ' in relation with 

 the line of the endostyle is, even more directly, with its ventral 

 end. On either side blood-vessels are seen crossing the interval 

 between the test and the mantle to join one or other of the two 

 vascular trunks in connection with the dorsal and ventral end of 

 the heart respectively. 



The mouth, in all Ascidians, occupies a point in the branchial sac 

 which is on the opposite side to the line of the ' endostyle,' and 

 to that of the ' thoracic sinus ' of Milne-Edwards, the so-called 

 'branchial arteries' of Savigny, which are here regarded as more 

 closely homologous with ' branchio-cardiac veins.' In this species 

 the mouth is much nearer the upper or anterior extremity of the 

 sac than it is in Ascidia Mentula. The digestive tract is seen to 

 describe two curves ; the first of these is made up by the stomach, 

 and the first segment of intestine which bends sharply back upon 

 it ; whilst the second is made up by this first segment of intestine 

 and the rectum. The concavity of the first of these curves looks 

 anteriorly, or towards the base of attachment of this erect species, 

 and away from the nerve ganglion; the concavity of the second 

 looks posteriorly, or towards its inhalant aperture. But if, as in 

 this description, the single ganglion of the Tunicata be regarded 

 as the homologue, not of the pedal but of the parieto-splanchnic 

 ganglia, if their branchial sac be also regarded as homologous not 



