Mr. A. Hancock on the Anatomy of Antiopa Spinolse. 31 



efferent or branchio-cardiac vessels are arranged in a peculiar 

 manner in Antiopa — differing alike from those in Eolis, in Doris, 

 and in Tritonia. 



The capillary portion of the vascular system is undoubtedly 

 as deficient in our animal as it is in the other Nudibranchiata ; 

 but I cannot speak from observation on this point ; neither have 

 I ascertained how the blood passes to the aerating surface, on its 

 return to the heart, though from analogy we cannot hesitate to 

 believe that it escapes from the arterial twigs into the tissues of 

 the various organs, thence filters as it were into the visceral cavity, 

 and then passing through orifices in the walls of that cavity, it 

 reaches the skin and branchial papillse on its way to the auricle 

 through the branchio-cardiac vessels. 



A small oval vesicle (PL II. fig. 1 m) lies immediately below 

 the pericardium, and opens into it, through its floor, rather in 

 front and on the right side of the median line. This vesicle 

 is the representative of that described by Cuvier, in Doris, as 

 communicating with the liver, and opening externally by a 

 minute orifice at the side of the anus ; and is the same which Dr. 

 Embleton and I have designated a portal heart in our commu- 

 nication on the anatomy of Doris *. In Antiopa Spinola: this 

 vesicle opens into the pericardium in the same manner as it does 

 in that genus, and in like manner is internally plicated. I have 

 not been able to examine it further in this species ; but from 

 analogy suppose that it may throw venous blood into the hepatic 

 network of tubes, and perhaps also within the sheaths that sur- 

 round the papillary glands. This is, I believe, the first time that 

 this vesicle or portal heart has been observed in the Eolididsef ; 

 and it proves in a striking manner the connexion of Antiopa 

 with the other two families of the order. 



Respiratory System. — The specialized breathing organ is com- 

 posed of the papillse arranged along the sides of the back, and 

 in front of the head. These in Antiopa are very large and 

 numerous, their external skin being exceedingly delicate. A por- 

 tion of the deteriorated blood, on its way to the auricle, will be 

 made to traverse the surface of the papillse ; but doubtless much 

 of the blood will pass at once through the skin to the heart, and 

 on its way be there partially aerated, as is the case in Eolis, in 

 Doris, and probably in all the Nudibranchs. 



No ovate vesicle was detected in the terminal portion of the 

 papilla, similar to that observed in Eolis ; though Mr. Alder in- 

 forms me that when the animal was alive, a distinct orifice was 

 visible at the apex, opening and closing at intervals. 



* Read at the meeting of the British Association held in Edinburgh, 

 1850. 



t A similar vesicle also exists in Tritonia Hombergii ; and since writing 

 the above I have likewise found it in Eolis papillosa . 



