110 THE VOYAGE OF H.M.S. CHALLENGER. 



component cells are flask-shaped, the thinner extremity shoving in between the pallisade- 

 shaped inner cihated epithelium. Moreover, among the Schizonemertea there appear to 

 be differences in the development of muscular tissue in the oesophageal wall, sometimes 

 the circumcesophageal blood-lacuna directly bathing this cellular coating, sometimes 

 {e.g., Cerebratulus corrugatus) a special muscular investment of conspicuous development 

 (PI. XIII. fig. 6, mto) being again present together with very strong nerves {nv). 



The passage from the oesophagus to the sacculated intestine is more or less gradual, in 

 the absence of any forward extension of the latter below the former, as was noticed for 

 the Hoplonemertea. 



Macrosco^^ic dissection enables us, nevertheless, to make a clear distinction between 

 these two jaortions of the gut, although microscopic investigation of transverse sections 

 shows that, histologically speaking, the passage is tolerably gradual. The cell layers of 

 the posterior portion of the intestine have been more than once sufficiently described 

 (see von Kennel (XVI), pL xviii. fig. 11), and it is not always easy to show them to 

 be provided with a nucleus or with cUia. StiU I do not hesitate to declare that the 

 whole of the intestine is ciliated, both the central passage and the lateral, generally sym- 

 metrical caeca. But this ciliation is often rendered inconspicuous by the fact that the 

 very elongated cells, composing the wall of this portion of the gut, are so overfilled with 

 small spherical globules as not only to render the ciliation invisible, but even to efface the 

 traces of the boundaries between the cells, so that in certain cases — both amongst Schizo- 

 nemertea and Hoplonemertea — it would seem as if the intestinal wall were replaced by a 

 compact mass of those globules enclosing the intestinal lumen between them. Similar 

 phenomena were observed by Lang (XVIII) in the Polyclada, and have been described 

 by other naturalists for other groups of Invertebrates. I will not here enter upon the 

 question of the relation of this phenomenon to the process of intracellular digestion, which 

 on a priori grounds may also be presumed to exist in the Nemertea, but will only add 

 that the nuclei of these high and elongated cells may in favourable specimens be 

 discerned, and are deeply situated, far away from the surface. 



Whilst strong vertical muscle-fibres pass from the dorsal to the ventral body-wall in 

 a lamellar arrangement, thus constituting what I have termed in a former publication (V) 

 the muscular dissepiments, placed alternately between the intestinal caeca, these caeca 

 themselves are destitute of any special musculature. The muscular lamellas just men- 

 tioned, together with the general body musculature, appear to be sufiicient to bring 

 about all the contractions in the intestinal wall needed for the progress along this 

 channel of the food swallowed. The intestinal epithehum itself is thus directly implanted 

 upon the gelatinous tissue, and this phenomenon is no less clear in the Schizonemertea 

 than in the Hoplonemertea (PL VIII. fig. 3; PI. IX. figs. 1-6; PL XV. figs. 7, 10). 

 -Among the latter Pelagonemertes is the most striking example of this, because of the 

 preponderance of the gelatinous tissue. It has been already noticed in a preceding 



