230 DESCRIPTIONS OF PREPARATIONS. 



weeks in the liver, in which it creeps about. It then escapes into the abdominal 

 cavity, and becomes encapsuled either on the omentum or mesentery. The 

 Cysticercus of some Tapeworms, e. g. of T. solium, is generally found in the connective 

 tissue of muscles, &c. In these instances the hexacanth embryo probably migrates 

 through the tissues, not through the blood-current. 



The changes undergone by the embryo are as follows. It grows in size, and 

 in the case of C. pisiformis becomes elongate, and the hooks are lost. The central 

 cells enlarge and become clear. The subcuticular muscles are differentiated, and 

 at a later period a system of more deeply placed muscles. Between the two layers 

 of muscles intervenes a layer of cells. It is from a meniscus-like thickening of this 

 cell-layer, which is developed at the anterior end, the end where the hooks remain 

 attached in C. Arionis, that the head and neck of the future Tapeworm are 

 developed. The head may be formed however, as in Archigetes Sieboldi, at the op- 

 posite end, the one at which Moniez asserts that it is always formed 1 . At the same 

 time a network of excretory vessels appears. It opens to the exterior by a pos- 

 teriorly placed pulsatile vesicle. The finer vessels end in ciliated funnels. When 

 the organism has attained a length of 4 mm. the central clear cells break down and 

 give rise to a central accumulation of liquid. In some instances this change 

 takes place at a much earlier period : in others, e. g. in Piestocystis or in the Cysti- 

 cercus Taeniae ellipticae, or of Tetrarhynchus, in a word, in the majority of Cestoda 

 the central cells do not thus liquefy 2 . 



When C. pisiformis is about 2 mm. long, the meniscus of cells above-mentioned 

 begins to develope. It grows inwards, pushing before it the deep layer of muscles 

 which form a receptaculum capitis. When it has reached a certain size, a de- 

 pression appears externally, and thenceforth the meniscus grows inwards as a hollow 

 cone. The cavity of this cone widens at its inner or deep end, and here the ros- 

 tellum, hooks, and suckers are developed ; but it is only when the cone is wholly 

 or partly evaginated that they appear in their ordinary shape. In the position in 

 which they are developed they are, as it were, inverted. When the head and neck 

 are evaginated the Cysticercus appears to be divisible into three parts, (i) the head 

 and neck proper, or scolex ; (2) the basal part of the invagination or hollow cone, 

 and (3) the proscolex or vesicle. When such an encapsuled Cysticercus is trans- 

 ferred to the stomach of a dog, the inclosing cyst is digested together with the parts, 

 (2) and (3) supra : and only the head and neck pass on into the intestine. Here the 

 head attaches itself by its hooks and suckers, and in forty-eight hours growth has 

 proceeded so far that there are well-marked indications of 12-18 joints. 



1 Leuckart states that the excretory system of Archigetes opens externally near the posterior 

 end of the scolex or sexual worm, i. e. the end to which the proscolex or vesicle is attached. The 

 excretory system of the scolex and proscolex, e. g. of a Cysticercus, opens externally at the end of the 

 proscolex opposite to that at which the scolex is attached. If Leuckart's statement is correct, it 

 shows that the scolex of Archigetes develops from the proscolex in an unusual position and tends, 

 therefore, to invalidate the assertion of Moniez referred to in the text. 



" Moniez states that the proscolex when i cm. long and less than I mm. broad divides trans- 

 versely, the two parts being connected by a slender pedicle which ruptures. The anterior half 

 develops the head : a rudiment of a head (?) was observed only once in the posterior half. The 

 point of attachment of the pedicle to the anterior half is marked by a persistent depression, the 

 foramen caudale. The fate of the posterior half is not known for certain. Non-division of a Cysti- 

 cercus is, according to Moniez, the reason why the proscolex sometimes attains such large dimensions. 



