BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 393 



The vapour of chloroform, if applied in sufficient quantity, causes them to cease 

 entirely, but they again commence vibration on the partial recovery of the animal. 

 Mr H. Goodsir thought that the fissures were the apertures of the male gener- 

 ative system, a supposition, as mentioned, scarcely requiring refutation. Prof. 

 Keferstein gives a very good summary of the views of previous observers, but, 

 while agreeing with none, he advances no new interpretation of these structures. 

 He concludes by criticising M. Van Beneden's statements, with which he dis- 

 agrees, but he has scarcely reviewed them at sufficient length. M. Van Beneden 

 observes that the cephalic fissures are furnished posteriorly with a pit leading into 

 a ciliated funnel, and that the lateral vessels when they approach the ganglia 

 swell out into vesicules (" ils se renflent la en vesicules"), which similate the 

 ganglia, and which lead their contents to the exterior by the ciliated funnel just 

 mentioned.* He considers that the central point of this apparatus lies imme- 

 diately beneath the ganglia on each side ; and he has seen, under compression, 

 the pit of the lateral slit adjoin a large canal, which terminated exteriorly by a 

 sort of funnel, and this led into a pouch behind the nerve-ganglia. He did not 

 see any vibratile movement within the vesicle ; and states his conviction that this 

 apparatus is similar to that in the Trematoda and Cestoidea. Thus, as Prof. 

 Keferstein says, he has nearly retrograded to the time of Huschke, who regarded 

 these fissures as connected with the lateral nerves, which he took for canals. In 

 his enlarged figure, f however, he represents the position of the cephalic sacs 

 fairly, but he has a large blood-vessel running to the exterior of the nerves, and 

 extending to the tip of the snout ; this, of course, is quite at variance with a true 

 interpretation of the structures in Borlasia. 



The cephalic fissures, as characteristic of the Borlasians, are absent in Meckelia 

 annulata, their places being supplied by two pale curved grooves on the dorsum 

 and two continuous transverse furrows on the ventral surface of the snout. The 

 furrows are richly ciliated. In the remarkable form from Balta, the snout is 

 surmounted by two curious frilled processes (Plate XIV. fig. 12, 6), which termi- 

 nate posteriorly in a long filament. Whether the latter, however, is a structure 

 sui generis, or only some normal constituent of the body (such as a nerve) in a 

 peculiar position, the state of the specimen forbids our determining. 



Cephalic Sacs. — At the posterior end of each lateral fissure, a funnel-shaped 

 tube (m\ Plate X. fig. 1) leads into a large globular structure (m), often of a 

 pinkish or reddish hue, and the apparent homologue of the cephalic sac in Omma- 

 toplea. This globular sac lies over the origin of the great nerve-trunk on each 

 side, and abuts so closely on the posterior prominence of the upper lobe of the 

 ganglion, as to have led some observers into the error of supposing it only a con- 

 tinuation of the ganglionic texture. Very carefully made preparations and 

 examinations of the adult animal, as well as observations on the young at various 



* Mem. de l'Acad. Roy. des Sc. de Belgique. f Op. cit. pi. i. fig. 5. 



VOL. XXV. PART II. 5 H 



