354 DR. T. S. COBBOLD, FURTHER OBSERVATIONS ON ENTOZOA. 
whose apices are directed backwards towards the body of the animal. The occasional 
absence of uniformity in the diameter of the sheath seems to me to be a point of some 
importance; for, had not my examinations extended over a considerable number of 
examples, I might have been led to the belief that I had to deal with several distinct 
forms of Trichocephalus. At first, indeed, this conclusion seemed inevitable, but finding 
intermediate conditions between perfect uniformity and the presence of a large flask- 
shaped distension near the free extremity, I can only suppose the variations to be due to 
the degree of protrusion at which the organ has arrived. In the accompanying woodcuts 
I have outlined a few of these appearances (figs. 1, 2, 3), which are intended for compa- 
rison with the simple condition of the sheath shown in fig. 10, Plate XXXIII. The penis 
itself is about three times longer than the everted sheath, the exposed portion measuring 
the ^th of an inch ; it is cylindrical, curved towards the tip, and coiled within the spirally 
twisted tail at its superior two-thirds ; the free extremity is scimitar-shaped, and rather 
sharply pointed (fig. 12). I did not observe any markings on its surface, but internally 
there were lines indicating the presence of a groove or internal tube, such as has been 
described as occurring in T. dispar. 
In regard to the organs of generation in the female, Kuchenmeister states that there 
are no external appendages in Trichocephalus comparable to those known to exist in the 
allied Trichosomata. So far, however, from this being the case, there is, in the present 
species at least, a remarkably prominent, and more or less hour-glass-shaped sheath ; 
this projecting vulva, if it may be so termed, being obliquely truncated at the free end, 
where it is also hollowed out, or rather inverted to give origin to the centrally enclosed 
vagina, whose orifice is somewhat constricted (fig. 13). The surface of this appendage is 
supplied with small spines, precisely similar to those described in connexion with the 
sheath of the male intromittent organ, the spines being likewise retroverted. This 
observation is confirmed by the statements of Mayer, who has described their occurrence 
at the vaginal orifice of T. dispar. Dr. Joseph Eberth, of Wurzburg*, however, in a 
recent number of Siebold and Kolliker's ' Zeitschrift,' rather incautiously denies the 
assertions of Mayer f. Dr. Eberth, having discovered a series of long conical processes 
within the vagina of T. dispar, totally unlike those described by Mayer and myself, has 
inferred that the structures in question are the same as those seen by us. I translate and 
quote his own words : — " According to Mayer, these are similar in form and size to the 
spines on the appendix of the penis. By means of these backwardly-directed points, the 
spicule when introduced into the vagina is said to be retained during the copulatory act . 
These statements," he adds, " are not correct : the villi of the vagina are larger than the 
spines of the male, and their points are, on the contrary, directed forwards." The latter 
part of this observation is, doubtless, quite true ; for it is evident that our little spines are 
entirely different from the curious villi discovered by Dr. Eberth. 
The ova, previous to impregnation, as in other Nematodes, are, at a certain stage, 
and irregularly triangular in outline ; the thin limiting membrane by which they are 
surrounded enclosing finely granular contents (fig. 14). In the perfectly developed egg, 
" Die Generationsorgane von Trichocephalus dispar," Zeitschrift for April 1860, p. 384. 
t Zeitschrift fur wissen. Zool., Band 9, s. 367. 
flat 
