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



This ciliated glandular structure is physiologically and homologically an 

 organ of great interest. It is entirely Ommatoplean in the condition just described, 

 since what is shown here in the complete form is only indicated in Borlasia by 

 the turning inwards of the margins at the junction of the two regions of the ali- 

 mentary canal. The granular glands and cells which coat the latter in Omma- 

 toplea arise (in the case of the cells, at least) on the sides considerably in front of 

 the posterior end of the oesophageal region — in some cases, indeed, almost touch- 

 ing the ganglia (Plate VIII. fig. 3), and besides, the first region has been demon- 

 strated to occupy a special pouch in which it rolls. The rich ciliation of this 

 oesophageal region, and the somewhat indistinct ciliary movements seen in the 

 posterior division of the alimentary chamber, are points of importance when con- 

 trasted with the arrangement in Borlasia, and show that from structure to struc- 

 ture the essential differences between the groups meet the inquirer at every step. 

 Tn Vortex, again, the homologue of this region is seen in the " Schlund" of the 

 German authors. 



The Digestive Cavity-Proper — The detailed description of the general cavity 

 of the worm (all within the muscles) given by M. de Quatrefages. shows that he 

 had no clear conception of this structure, for, after explaining the hypothetical 

 transverse diaphragm, to which we have already alluded, he goes on to say,*— 

 " Le reste de la cavite generale occupe tout le corps proprement dit ; mais les 

 cloisons verticales auxquelles sont suspendus les organes generateurs le parta- 

 gent entrois chambres distinctes, Tune mediane, qui renferme le tube digestif 

 dans une portion de son entendue; les deux autres laterales, dans lequelles 

 flottent les ovaires ou les testicles, et qui a l'epoque de la reproduction se rem- 

 plissent d'ceufs ou de zoospermes." In his figuresf the scalloped shaded portion, 

 which he terms " ovaires ou testicles," is, as Prof. Keferstein has pointed out, the 

 glandular wall of the digestive cavity. I am at a loss to understand how M de 

 Quatrefages did not correct his error on contrasting his figures of the male and 

 female elements in his Nemertes balmea (0. gracilis), for the very same organ is 

 made in the one case ovary, and its gland-cells developing ova, and in the other 

 respectively testicle and sperm-cells. Dr Johnston J recognised the structure as 

 " a close series of vesicles or cells, formed, in the true Nemertes. apparently by 

 the folds of a membrane." The caeca, he adds, are always full of some opaque 

 matter, which varies " in intensity at least according to the nature of the 

 animal's food." He thought the structure was connected with the digestive sys- 

 tem, though not in communication with the proboscis (his alimentary organ). 

 Dr Willtams§ had also an inexact idea of this cavity, for he speaks of it as a 

 great spongy mass, or "great alimentary caecum, " which commences anteriorly 



* Op. cit. p. 152. t Op. cit. e.g. pi. xviii. fig. 1, and pi. xix. fig. 1. 



+ Mag. Zool. and Bot. vol. i. p. 532. § Report Brit. Assoc. 1851, pp. 244-5. 



