DIGESTIVE SYSTEM. 77 



In A. pulcJier the granular glands of the oesophagus are distinct and large ; and in T. mela- 

 nocephala the organ is curiously narrowed posteriorly. In Nemertes carcinop/iila it is short, 

 nearly globular under moderate pressure, and presents a very distinct terminal aperture. It is 

 also conspicuously tied in this species by strong transverse bands posteriorly. 



This ciliated glandular oesophageal region is physiologically and homologically an organ of 

 great interest. It is peculiar to the Enopla in the condition just described, since what is shown 

 here in the complete form is only indicated in the Anopla by the turning inwards of the margins 

 at the junction of the two regions of the alimentary canal. The granular glands and cells which 

 coat the latter in Amp/iiporus arise on the sides considerably in front of the posterior end of the 

 oesophageal division (Plate XIV, fig. 1), being collected in transverse section (Plate XI, fig. 3) 

 chiefly on the ventral surface of the organ. The first (oesophageal) region, besides, occupies a 

 special space in which it rolls. Its rich ciliation, and the somewhat indistinct ciliary movements 

 seen in the posterior division of the alimentary system, are points of importance when contrasted 

 with the arrangement in the Anopla, and show that from structure to structure essential dif- 

 ferences between the groups meet the inquirer at every step. 



c. The Digestive Cavity Proper. 



After explaining the hypothetical transverse diaphragm, to which I have already alluded, 

 M. de Quatrefages proceeds to observe — " Le reste de la cavite generale occupe tout le corps 

 proprement dit ; mais les cloisons verticales auxquelles sont suspendus les organes generateurs le 

 partagent en trois chambres distinctes, Pune 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 Pepoque de la reproduction se remplissent d'ceufs ou de zoospermes." In his 

 figures the scalloped shaded portion, which he terms " ovaires ou testicles/' is, as Professor 

 Keferstein pointed out, the glandular wall of the digestive cavity. Thus 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 recognized 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 system, 

 though not in communication with the proboscis (his alimentary organ). Dr. T. Williams 

 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 immediately behind the hearts (ganglia), under 

 the character of a caecal end, and as " a perfectly closed sac, containing a milky fluid/' The 

 walls of this cavity, he states, act upon the exuded food, after its passage through the coats of 

 the " oesophagus." He is correct in denying the ovarian character of the organ, and in showing 

 that the so-called ova consist only of oil-globules. Dr. Max Schultze described it as a straight 

 canal in Tetrastemma ohscurum, ciliated on its inner surface, and opening anteriorly and pos- 

 teriorly ; he also figures its cells — altered by extrusion into the water. 



The digestive cavity in the Enopla is a somewhat moniliform or pinnate canal, in so far as 

 its surface is increased by the numerous diverticula, which are best observed on the ventral 

 surface. It appears under pressure in Tetrastemma (Plate XIV, fig. 1) as a lobulated glandular 



