THE ANATOMY OF A NEW SPECIES OF BATHYDORIS. 201 



it reaches the right corner of the pericardium to empty itself into the auricle. The 

 circular sinus is also represented in the Pleurobranchids, where it also opens into the 

 efferent vessel, but takes a wider sweep round the body. In the Dorids it is repre- 

 sented by the two lateral sinuses, which there, however, enter the auricle separately 

 and directly. 



(7) The Blood Glands, (b.g.' and b.g." Figs. 8 and 9.) 



The structures commonly called " blood glands " are characteristic of some Tecti- 

 branch families (Bullids and Pleurobranchids) and of the Dorids. They are lymphatic or 

 phagocytic glands situated on the course of the cephalic artery and supplied by it. In 

 the Dorids they lie in the head region near the brain, but in the Tectibranchs they are 

 placed further back. In Bathydoris they form two separate masses united to the wall 

 of the kidney. It is of some interest to note that in the Prosobranchs possessing them 

 they are also associated with the kidney, so that in this, as in many other respects, 

 Bathydoris presents features more primitive than the true Dorids, the equivalents of 

 which are found among Tectibranchs rather than Nudibranchs. As already mentioned, 

 Bergh and Eliot confused the unusual salivary glands with the blood glands, the 

 identity of which they did not recognise. 



The Respiratory System. 



As already indicated in connection with the vascular system, the general pallial 

 respiration is rendered more effective by the papillary outgrowths, and the blood so 

 oxygenated returns into the circular sinus. The special respiratory organs or branchiae 

 are two tufts placed symmetrically on a transverse ridge in front of the anus. Each 

 tuft stands on a broad base or stalk in such a way as to give the appearance of a roughly 

 pinnate condition. The lobate units of the tuft resemble the pinnae of the gill of 

 Pleurobranchsea, being laminate on opposite faces of a wide rhachis, while the afferent 

 and efferent vessels occupy its edges. The laminae vary in size from mere ridges across 

 the face of the rhachis to longish leaves which may themselves be provided with laminae. 

 In this way an irregular bipinnate condition is simulated. It will be seen that, by 

 narrowing the rhachis so as to bring the ascending and descending vessels nearer 

 together and regularising the pinnation, the Dorid plume would be produced. On the 

 other hand, if the laminae were equal in size and the tufts stretched along the ridge in 

 a regular row, the sessile portion of a Pleurobranchid ctenidium would result. The gill 

 of Bathydoris brownii would therefore appear to be in a condition intermediate between 

 a typical Dorid rosette of plumes and a Tectibranch gill. There is, however, no indica- 

 tion of a circumanal circlet either in the gill itself or in the underlying vessels, and though 

 the tufts are provided with muscles capable of reducing their height, they cannot be 

 retracted below the general level of the integument. 



