REPORT ON THE NEMERTEA. Ill 



paragraph that this jelly appears to be somewhat denser, and that at any rate it 

 more strongly imbibes staining reagents, all round the circumference of the intestinal 

 epithelium where this is implanted upon it. 



As to the oesophagus of the Hoplonemertea, I wish to observe that it is less thick and 

 massive than that of Eupolia and the Schizonemertea, and more resembles the simple 

 arrangement of Carinina. Its wall is generally only one cell-layer thick, and a distinct 

 cuticula, as was noticed in Carinma, may also be often observed here. Fig. 1, Oe, of 

 PI. X., representing a section of the oesophagus of Amphiporus marioni, gives a very fair 

 representation of it. Outside the oesophageal epithelium there are indicated in this figure a 

 layer of flattened cells which I at first expected to form an outer tunic to the oesophagus. 

 Closer investigation revealed the presence of these cells in all the tissues — they may also 

 be seen in the basement layer B of the same figure — and at the same time convinced me 

 that these unicellular bodies are parasitic organisms. They infest all the tissues of 

 their host, and are more abundantly heaped together just outside the oesophageal 

 epithelium, where nutritive substances may be expected to be more plentiful. Curiously 

 enough, they were also noticed in the smaller specimens of Amphiporus marioni. 

 Similar cases of specimens of Nemertea infected with unicellular parasites were noticed 

 by me on other occasions. There is another case amongst the Challenger material (see 

 p. 48), but there the parasite is much larger than in Amphiporus marioni, and 

 altogether difi"erently constituted. It agrees with the former only in the fact of its 

 presence in all parts of the tissues. 



These parasites diff"er from others which are found in the lumen of the intestine, and 

 which have already been noticed by former observers. 



Another view of the Hoplonemertean oesophagus is given (in longitudinal section) 

 in PI. XV. fig. 20. Here, too, the comparative thinness of the walls is conspicuous, 

 and the connection with the posterior gut portion which stretches forwards under it, 

 is clearly indicated. 



In Pelagonemertes the last mentioned phenomenon could not be observed. The sec- 

 tions through the mouth^and oesophagus were, however, not intact, because of the macro- 

 scopic dissection to which the specimen had previously been subjected by M'Intosh. 



As to the ca3ca of the posterior body region little remains to be noticed, but that they 

 are more regularly distributed as we approach the tail, i.e., the region where new caeca 

 are being continually formed. Their metameric and paired arrangement is here more 

 evident than further forwards, where the degree in which they are filled with food par- 

 ticles may be more or less difi"erent, and may thereby become the cause of a partial, but 

 not very common, asymmetry. 



The innervation of the intestine was for the greater part described in the paragraph 

 treating of the nervous system. It may be remarked here, in addition, that in transverse 

 sections of the foremost portions of the oesophagus it is very easy to detect the consider- 



