THE ANATOMY OP A NEW SPECIES OF BATHYDORIS. 199 



The asymmetry of position mentioned above is an insignificant matter compared 

 with the structural asymmetry shown by the heart itself. The typical Dorid heart is 

 roughly an isosceles triangle with three efferent ducts opening into its base, the efferent 

 branchial in the middle and the two lateral integumental sinuses at the corners. The 

 auricle of Bathydoris, on the contrary, receives but one efferent vessel, which enters it 

 at the right-hand side, the efferent branchial vessel and the lateral sinuses being con- 

 fluent outside the pericardium altogether, as in the Pleurobranchids. The left side of 

 the auricle is fused for some distance with the pericardial wall, along which it sends a 

 muscular wing. This asymmetry, as we shall see later, is only one of many pre-Dorid 

 and ancestral opisthobranch features exhibited by Bathydoris. 



(2) The Arterial System. 



Although the arterial system possesses no striking feature, it is proposed to describe 

 it somewhat fully, because no comprehensive account exists of the arterial system of 

 any Dorid except Hancock and Embleton's account of Doris tuberculata in their 

 famous article in the Philosophical Transactions of the Royal Society. The ventricle 

 (v.) is immediately followed by a large aortic bulb (a.c.) from which arise the renal 

 arteries (see kidney), as well as vessels to the intestinal loop, the gonad and the 

 periphery of the liver mass lying below. The aortic bulb is continued forwards as the 

 main cephalic artery (cart.) This gives off on the left the visceral artery (v.art.), 

 running below the intestine and supplying the liver, stomach, and oesophagus. In 

 fig. 9 the arterial trunks lying below the outlined viscera are dot-shaded. After 

 giving off the genital arteries (g.art.) on the right, the cephalic artery bifurcates, one 

 branch passing over the oesophagus to the left and the other below the buccal mass to 

 the right. The left branch provides both salivary glands (sal.g.), the brain (cer.art.), 

 and the buccal muscles of both sides, while the right branch goes direct into a spacious 

 infra-pharyngeal lacuna (lac), in which the left also ends. This lacuna was also found 

 in Doris tuberculata. It should be noted that the cephalic artery forms a complete 

 collar round the oesophagus and buccal bulb. From the central lacuna under the bulb 

 arise a number of vessels. A median vessel passes straight up into the bulb (bucart.) ; 

 three run forward into the lips (lab.art.) and floor of the mouth, while a broad median 

 vessel dips into the foot and bends backward in its substance, to continue throughout 

 its length as a median pedal artery (ped.art.) 



(3) The General Hsemocosle. 



The irregular lacunar blood-space in which lie all the viscera is in Bathydoris 



nowhere spacious. It receives the blood that has passed through the tissues from the 



arteries, except the renal, gonadial, and hepatic blood, which is collected in another 



way already indicated in the description of the kidney. The hsemocoelic blood passes 



partly into the gills and partly into the dorsal integument, but the proportion of blood 

 TRANS. ROY. SOC. EDIN., VOL. L. PART I. (NO. 6). 27 



