G34 MR. E. R. LANKESTER ON SOME LOWER ANNELIDS. 



a warty corrugated appearance. These clear " cells" or vesicles are found occasionally in 

 the integument of various Oliffochseta, where they appear to be much more localized than 



^UIUCIXU VS. ,«*J.* V ~~ — 



here, or rendered less obvious by the intervention of other structures. In JEolosoma the 

 translucent red bodies in the integument are undoubtedly identical structures ; in JPar- 

 thenope of Schmidt, or Ctenodrilus of Claparede, and in Thysanoplea of Schmidt similar 

 bodies appear to be very numerous ; whilst the clear vesicles in the integument of very 

 many Planarian worms belong to the same order of structures. 



Beneath these bodies we come upon the muscular body-wall. The bristles of the 

 bristle-bundles are colourless and quite structureless, but apparently horny. The stem is 

 scarcely sigmoid, and swollen slightly at its insertion ; the apex is turned at right angles 

 to the stem and is bifid, forming a small prehensile organ (fig. 15). The average length 

 of the cephalic bristles is 2^0 inch, being nearly the same as the average diameter of the 

 worm when not flattened by pressure. The abdominal bristles are about 4^0 i^ch m 

 length, or less. Their number and characteristic distribution has been already spoken of. 

 In growth they appear at first as straight bookless stumpy bristles, and are even then, 

 when near the posterior extremity, used for prehension. Leydig has stated that each 

 bundle is in reality double, as may be seen by the use of an acid. I am quite sure that 

 this is not true with regard to Ch. limncei. 



Muscles. — The muscular layer of the body-wall is not, in these asexual forms, percep- 

 tibly divided into transverse and longitudinal layers, though it contains fibres of both 

 directions, as may be seen by the use of acetic acid. There is considerable differentiation 

 of the muscular layer in connexion with each bundle of bristles, the fibres being so 

 arranged that the bundle of bristles may be spread out like a fan with the booklets 

 pointed in any direction. The muscles of each pair of abdominal bristle-bundles do not 

 act separately, but the whole series seems to be moved by the same set of muscles, whilst 

 the cephalic pair of bundles are distinct. Many fibres exhibit a cellular character (fig. 28). 



The pharynx is worked in its sucking-movements by very numerous fibres passing 

 from it to the neighbouring body-wall, which is cellular. 



No special structure can be assigned to the muscular fibre ; it appears merely as a 

 substance broken up into elements, each one of which is too small or indefinite to present 

 any character. 



Alimentary Canal— The mouth cannot be said to be exactly terminal, as in the figure 

 given by Leydig of Ch. diaphanus. It is capable of assuming a terminal position when 

 stretched and widely open ; but when closed a portion of its dorsal mai gin projects beyond 

 it to a small extent, representing the « prostomium " or « Kopflappen." This lip is mus- 

 cular and very moveable, and is supplied with many nerves from the prostomial or supra- 

 cesophageal ganglion (figs. 13 & 25). The mouth opens into a very extensive and highly 

 elastic pharynx, which, as before said, is closely connected to the body-wall by muscular 

 fibres, and by its rapid alternate expansion and contraction draws in the Infusoria, Cer- 

 carue, &c. on which the worm feeds. At the junction of pharynx and oesophagus is a bul- 

 bous enlargement, which lies above a sort of nerve-ganglion. The food having been drawn 

 into the pharynx, the mouth is tightly closed, and by a contraction the mass is forced 

 tnrough the short, narrow, and elastic oesophagus into the stomach (figs. 19-22). The 



