402 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



form of the latter, as well as the error into which those authors have fallen who 

 have confounded the sacs in the adult animals with posterior ganglionic enlarge- 

 ments. The sacs open by their ducts at the posterior part of the cephalic fissures 

 (b), and the ciliary action can be traced inwards from these points. The oesopha- 

 geal division (j) of the digestive canal is distinguished by its pallor, more evident 

 ciliation, and the well-defined border of the succeeding opaque region (/). The 

 proboscis (a) is marked by a central streak of papilla?, and, after tapering poste- 

 riorly, it curves forwards, and disappears. The proboscidian sheath (o) is observed 

 to be banded here and there anteriorly by transverse bridles ; and a clear line is 

 occasionally visible on each side of the opaque alimentary tube, as if from circu- 

 latory undulation. An anal papilla (Plate XII. fig. 7), with a ciliated line con- 

 necting it with the digestive cavity, is also apparent. 



Shortly after reaching the degree of advancement shown in Plate XIII. fig. 5, 

 the young Borlasians leave the gelatinous masses, and congregate at the water- 

 line. Hundreds now perish from want of sufficient food, which in their 

 native haunts is doubtless both abundant and suitable, while in the artificial cir- 

 cumstances and confined vessel it is denied them. Two and a half months after- 

 wards the young animals are found still of the same whitish hue, and possessing 

 only two eyes, rarely with an additional pigmentary fragment. The proboscis 

 has much increased in size ; indeed, at this time it has attained a comparatively 

 larger development than the digestive cavity, which is in active use, since the 

 young animal is entirely dependent on its own exertions for a supply of food. 

 The oesophageal region is very distinctly marked, though its dimensions are 

 proportionally small when contrasted with the length of the head ; at present 

 it is not a quarter the length of the latter, whereas in the adult it is several 

 times longer. Its space is also considerably encroached on by the large cephalic 

 sacs. 



At a further stage of development the animal is much elongated, yet still 

 possesses only two eyes. In this condition it has, doubtless, been mistaken for 

 the representative of a different genus, and is probably that referred to by Dr 

 Johnston, under the name of Ceplialothrix ( Vermiculus lineatus, Dalyell). 



M. de Quatrefages observes that the reproductive organs are digitate in 

 Borlasia angliie, and figures them after this manner ; * but such is scarcely a cor- 

 rect definition ; neither have any cilia been detected in connection with these 

 structures. Indeed, he has probably mistaken the digestive canal and its saccu- 

 lations for the reproductive system, as he mentions that out of season the caca 

 are filled with a fluid more or less opaline. M. Van Beneden remarks that 

 the ovisacs contain from one to a hundred ova in his Nemertes communis ; but 

 although deposited in a membranous sheath in September, no change had ensued 



* Op. cit p. 182, p]. xx. fig. 8. 



