326 ANIMAL PAEASITES. 



by the cessation, at tins spot, of the parenchymatous contents 

 of the animal (intestine and muscles), and the rapid 

 approximation of the two empty layers of the epidermis of the 

 animal. As the worm is round, and a small space still remains 

 between the complete fusion and the closest possible approxi- 

 mation of the lamellse of the skin, and the shadows of these two 

 lines do not fall exactly in one. level, the whole presents the 

 appearance of a band. If, as appears to be the case, Wedl 

 intended something of this kind by the expression " structureless 

 layer/' I perfectly agree with him in his opinion. 



Body. As the Trichosoma consist of a thin filiform, and 

 thick, catgut-like portion, so also do the Trichocephali, only that 

 in the former the anterior, and in the latter the posterior, part of 

 the body is the thickest. Only the mature females are distin- 

 guished by their external form from the males. Thus, the male 

 coils up both the anterior part of the body and the abdomen in 

 spiral turns, in the same way as the other nematode worms. 

 Hence we always meet with the male more or less in the form of 

 a spiral or of a repeatedly twisted cord. It would be difficult to 

 judge from this how the worm could have been characterised by 

 the name of whip-worm (Peitschenwurm), if we were not obliged 

 to admit that this name is very suitable to the females, and 

 these, being larger, were probably first discovered. Thus the 

 abdomen of the latter may be very well compared to the straight, 

 thick, stiff, short, stick or stem of a whip, to which the slender 

 body is attached like the lash of the whip (as in a dog-whip or 

 sledge- whip). The anterior thinner part presents no further dif- 

 ferences in the males and females. The head is pointed towards 

 its anterior extremity, but always terminates somewhat flattened. 

 Even when the worm is treated with white of egg, and in fluids 

 whose contact with the worm does not usually cause the emission 

 of sarcode globules, we often perceive, at the extreme tip of the 

 head, the protrusion of a small, hyaline, onion-like structure, which 

 passes off in an obtusely conical form anteriorly, and which I rarely 

 saw wanting. This appears to me to show that we have to do in 

 this case with a peculiar structure, capable of eversion and inver- 

 sion, belonging to the worm, and not with a drop of sarcode. This 

 apex of the head of the worm is perforated by a mouth, which is 

 followed by a long, straight, rather cleft-like apparatus. After run- 

 ning about 0-8 mill. = O4"' in the male, the digestive apparatus 

 becomes enlarged, and forms very narrow dilatations and coustric- 



