146 Transactions of the 



attached to the dorsal surface, and the nervous system as lying on 

 the ventral side of the body, this single branchial aperture would be 

 on the left side. I did not see any streams of water, but if the 

 quadrangular figures really represent stigmata, then it is to be sup- 

 posed that the water would pass through these to enter the cavity 

 of the body, and then make its exit through the branchial aperture. 

 This is evidently quite a difierent arrangement to that in A. Jiabel- 

 lum, in which species, as described by Professor Huxley,* the two 

 branchial apertures communicate directly with the branchial 

 chamber. The branchial chamber is traversed by a ridge which 

 runs obliquely across from about the middle of the endostyle to the 

 commencement of the oesophagus ; this ridge is provided with longer 

 cilia than the remainder of the cavity. I did not see that it divided 

 into two branches at the anterior part, as mentioned by Professor 

 Huxley in A. fiabellum.] 



The endostyle is very thick ; on a side view it presents a fissure 

 down the centre, which makes it have the appearance of a double- 

 fanged tooth ; it extends backward nearly as far as the rectum. 



The oesophagus commences as a gradual tapering of the branchial 

 chamber ; it passes backward towards the posterior end of the body, 

 and there turning slightly towards the dorsal surface it enters the 

 stomach. It is ciliated throughout. The ciliated ridge enters its 

 anterior extremity ; in fact, there is no line of demarcation between 

 it and the branchial chamber. 



The stomach has the form of a circular disk, which occupies 

 nearly the posterior half of the right side of the body ; at its postero- 

 ventral side there is a deep notch, into one side of which the oeso- 

 phagus enters. Its postero-dorsal walls are thicker than the antero- 

 ventral. The convexity on this latter aspect fits into a corresponding 

 concavity formed by the branchial chamber and the oesophagus. 

 That part of the stomach which has thicker walls appears to be 

 glandular, and is provided with numerous hemispherical papillas. 



The intestine has the appearance of four oval chambers with 

 thick walls; when the contents are not passing from one to the 

 other they seem to be perfectly distinct, and no apertures of commu- 

 nication are visible ; I will call these chambers Nos. 1, 2, and 3. 

 Commencing from the stomach, No. 1 is situated on the left side 

 of the body even with the an tero- ventral wall of the stomach, with 

 which it communicated by an aperture coextensive with its length ; 

 in fact it appeared to be nothing more than a pouch of the stomach 

 directed towards the left side, and evidently corresponds to the left 

 lobe of the stomach in A. Jiabellum ; it would not have been here 

 classed with the intestine had it not been for the circumstance 

 that the faeces first begin to be formed therein. No. 1 opens by 

 its posterior extremity into chamber No. 2, which is of the same 



* Loc.cit. t 'Diil. Tntus.,' 1851. 



