DIGESTIVE SYSTEM. 75 



are analogous to those of the sponges, whose microscopic anatomy has been so excellently inves- 

 tigated by Dr. Bowerbank. Indeed, the morphology of the stylets in the Enopla offers 

 elements for deeper reflection than even the hooks and bristles of the higher annelids, which are 

 often so diagnostic of genus and species. 



Besides the developing organ the proboscidian chamber contains (unless in cases where it 

 has been violently expelled) the rejected proboscis ; and it is an interesting sight to observe a 

 fully-developed structure floating freely in the chamber, and still endowed with contractile power, 

 while the new proboscis has advanced to the stage of the advent of stylets. The discarded organ 

 soon becomes opaque, appearing reddish by transmitted light, and the stylets leave their positions. 

 As there is no mode of exit after the new proboscis has begun to develop, the aborted one can 

 only (not to speak of rupture) be removed by disintegration and absorption ; and hence in the 

 proboscidian chambers of such animals there is a vast increase of cells, granules, and granular 

 debris. 



6. Digestive System. 



a. The Mouth. 



Dr. Max Schultze, almost alone amongst foreign authors, seems to have noticed the true posi- 

 tion of the mouth in his Tetrasfemma obscurum. It forms a slit on the ventral surface immediately 

 behind the aperture for the proboscis (Plate III, fig. 8, w; and Plate XIV, fig. 11, w). The two 

 openings are especially distinct in Amphiporus hastatus and Prosorhochmus Claparedii. In 

 animals which have been subjected to chloroform, the oesophageal apparatus is occasionally pro- 

 lapsed through the mouth under pressure. The observations on this point have been often 

 repeated, out of deference to the distinguished continental authors who hold different views, but 

 I have never seen any deviation, and it is hard for the oral aperture to exist in the free portion of 

 the oesophageal apparatus behind the ganglia. There is thus a marked distinction between the 

 Enopla and the Anopla, the mouth in the first group opening quite in front of the ganglia, while 

 in the other it is situated considerably behind the ganglia. 



b. (Esophagus. 



Though no transverse muscular plate, as described by M. de Quatrefages, occurs at the 

 anterior part of the body of the worm, yet there exists a very distinct and comparatively large 

 ciliated oesophageal chamber. The figures of the supposed transverse plate, indeed, given by the 

 French author, show a degree of doubt, since in one drawing both wavy and longitudinal 

 fibres are represented, while in another there are only transverse fibres. The wavy and longi- 

 tudinal lines no doubt owe their presence to those actually existing in the oesophagus. Dr. 

 Johnston indicates this structure in a figure of T. melanocephala, and he refers to it under 

 A. pulcher thus : — " Immediately under the hearts " (ganglia) " we observe a large, somewhat 

 muscular viscus, apparently hollow, and lying in the course of the intestine, but seemingly 

 unconnected with it. Of its office and nature I can form no opinion ; but I may remark, that in 

 all the species a greater duskiness in its site shows that a similar organ exists in all." Pro- 



