4 ONCHIDIADiE. 



pale yellowish-grey colour. The head bore two short 

 retractile tentacles, with eyes on their swelling tips ; these 

 are set above the rounded pale oral lobes or veil. 



The following very interesting remarks on the anatomy 

 of this Oncliidium, have been kindly communicated to us 

 by Mr. Albany Hancock. 



" I have not yet completed my dissections of this ani- 

 mal, but from what I have already ascertained, it is evi- 

 dent that it is formed on the type of the Pulmoni/era. 

 The ganglia of the nervous system have much the same 

 arrangement as they have in Arion. But the digestive 

 apparatus shows one or two interesting modifications. 

 The buccal mass is well developed ; there are no horny 

 jaws ; the tongue is broad, and composed of upwards of 

 seventy transverse rows of obtuse, slightly curved teeth 

 — each row contains one hundred and eight teeth, and 

 is divided by a minute central tooth of a triangular form, 

 bearing a single obtuse spine. The reproductive organs 

 are conjoined in the same individual ; the male intro- 

 mittent organ is, however, placed at the right side of 

 the head, whilst the other parts are situated at the pos- 

 terior extremity of the body. The male and female parts 

 are nevertheless connected by a long, slender duct, buried 

 in the muscles at the side of the foot. 



" The most interesting feature in the anatomy of On- 

 chidium, is the position of the heart and breathing-organ 

 in relationship to each other. The lung being placed, 

 in this animal, at the posterior extremity of the body, 

 has, consequently, the heart in front of it. In Arion, 

 Helix, and, probably, in all the other Pulmoni/era, the 

 blood-propelling organ is situated behind the breathing- 

 apparatus, which, in these animals is placed in an an- 

 terior position. Thus we find that Onchidium differs 



