328 The Whip-Worm. 



rendered more apparent. On one side of the longitudinal band 

 Dujardin also figures and describes a series of minute super- 

 ficial papillas, which he associates with a festooned border of 

 the band. We have not observed these prominences, and the 

 festooned markings are manifestly due to the subjacent convo- 

 lutions of the oesophagus (b), being singularly uniform in size 

 and disposition. In the fresh state the dermal rings (c c) are 

 beautifully distinct. They are said to extend all round the 

 filamentary neck, but we found them ceasing at a little distance 

 apart from either margin of the longitudinal band. Midway 

 between the latter and the serrated border of the neck there 

 exists internally a double row of oval corpuscles (cl d), but no 

 vessels or fibres were observed in connection with them. As 

 regards the reproductive organs, the first thing that strikes 

 one is the unusual length of the intromittent organ and its 

 membranous sheath. This character is believed to be dis- 

 tinctive ; at all events, it departs very materially from what is 

 observable in Trichocephalus dispar, where the sheath forms 

 externally a funnel-shaped tube. The organ in question is 

 also itself included in a sheath-like, muscular mass, apparently 

 concerned in the evolution of the intromittent organ ; its free 

 end is shown in fig. 5 (a). We have never seen this muscle 

 exserted, but the cloacal opening (b) is sufficiently capacious to 

 give it free passage, if necessary. The everted part of the 

 sheath (c) measures about the T ^ of an inch in length ; being 

 perfectly transparent, not always uniform in breadth, but 

 covered throughout its entire extent with minute, conical, 

 sharply-pointed spines, whose apices are directed backwards 

 towards the body of the animal. 



The occasional absence of uniformity in the diameter of the 

 sheath seems to us to be a point of some importance ; for, un- 

 less our examinations had extended over a considerable number 

 of specimens, we might have believed ourselves to have found 

 several distinct forms of Trichocephalus. At first this con- 

 clusion seemed inevitable ; but, finding several intermediate 

 conditions between that of a simple cylinder, on the one hand, 

 and that of a tube furnished with a large flask-shaped dis- 

 tension near the free extremity on the other, it became evident 

 that the variations of outline were only due to the degree of 

 protrusion or contraction to which the organ had, in either 

 case, attained. 



To make these appearances clearly understood we have 

 added a woodcut, which should be compared with fig. 4 in the 

 plate, where the sheath is extended to the utmost. In the 

 cut the corresponding letters have the same meaning in both 

 figures, and they bear the following indications: — a, epidermis; 

 b, cutis ; c, caocal end of the testis; d, seminal duct; e } intestine; 



