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



by Frey and Leuckart,* Kolliker,| Max Schultze, J Van Beneden,§ Kefer- 

 stetn,|| and lately they and certain ova in this species by the author ;^[ so that 

 the subject need not be further alluded to here, save to observe that they are 

 strictly confined to the region behind the streaked oesophageal division of the 

 digestive tract, that they hang freely into the cavity, and that the ova mentioned 

 in the last paper probably may not be connected with this particular species of 

 parasite. The occurrence of these ova, however, in specimens so widely different 

 in habitat as St Andrews and South Devon, shows that there is some constancy 

 in their presence. The parasites occur in young specimens scarcely a quarter of 

 an inch in length, and vary in size. When the animal has regained its condition 

 in its native haunts after spawning, the granular cells of the digestive chamber 

 become largely developed, so that in transverse section the body is rounder, and 

 the entire central region filled up by the mass, with the exception of an irregular 

 fissure in the centre ; whereas considerable atrophy of these elements occurs 

 during long confinement, or the exigencies of reproduction. Towards the poste- 

 rior end of the worm, the tract becomes considerably diminished in size, and, in 

 the living animal, more evidently ciliated when viewed from above. The minute 

 structure of the wall of the cavity (Plate XII. fig. 10) has a considerable resem- 

 blance under pressure to that of the ciliated oesophageal region in Ommatoplea, 

 having a basement-substance, in which are imbedded a vast array of granular 

 glands, and with the inner surface richly ciliated. The contents of the glands 

 (Plate XIII. fig. 7) consist of granular cells and globules, which readily escape 

 from the free border of the organ, and are often ejected per anum. 



In Cephalothrix the lips of the oral aperture are frequently pouted out- 

 wards in the form of a short funnel, so that the animal resembles an elongated 

 Distoma, and the ciliation of the entire canal is more apparent than in Bor- 

 lasia. Some circular fibres around the mouth are evident in this genus, and 

 probably exist also in Borlasia. The general arrangement in transverse section 

 is seen in fig. 3, Plate X., and the same gregariniform parasites before mentioned, 

 as well as an Opalina, likewise occur. In minute structure, the first or oeso- 

 phageal portion has a much more lax and cellular aspect than the succeeding 

 densely granular region ; and from the translucency of the animal, the distinc- 

 tions in this respect are more exaggerated than in Borlasia. In one specimen 

 sent from St Andrews in April, the digestive chamber was coloured of a fine pea- 

 green instead of the usual pale pinkish hue — a state due to the uniform tinting of 

 the cellular elements. 



It may now be proper to refer to the presence of another parasitic animal 

 which was found in several specimens of Borlasia olivacea from St Andrews in 



* Beitrage zur Kenntniss, &c. f Zeitsch. f. wiss. Zool. bd. i. pp. 1 and 2, taf. i. fig 4. 



J Beitrage zur Naturges. Turb., &c. § Op. cit. \\Op. cit. p. 70. 



% Quart. Jour. Micros. Sc. <fcc, April 1867. 



