190 ANIMAL PARASITES. 



and a small globular vesicle, adhering to the inner wall of 

 the Echinococcus, is formed, presenting an external structure- 

 less epidermis and an inner granular layer. In the granular 

 layer of these processes which have been dilated into vesicles, 

 we observe vessels, which are connected with those of 

 the Echinococcus-xes'icle, and, subsequently, when the small 

 vesicles have attained a certain size, again lead to the formation 

 of processes in themselves. Thus, from these new (4 — 10) pro- 

 cesses the scolices of the Tcenia are produced, with a general 

 increase in the size of the capsule. This occurs essentially in 

 accordance with the same type as in the Cysticerci, with the 

 sole difference that, as Leuckart has pointed out, the cephalic 

 processes become hollow from the inner end, which is turned 

 towards the cystic worm, and not from the wall of the vesicle. 

 The immediate neighbourhood of this cavity is also contracted 

 with the rest of the parenchyma of the cephalic process, with- 

 out ever forming a caudal vesicle, which would be cast 

 off during the transition into the strobila. The wall of 

 the vesicle, in which the head is inverted, afterwards forms 

 the hinder part of the young Tcenia. If anything is lost in 

 this transformation, it can onlv be the rudiments of the stem 

 which occurs in all individual scolices of Echinococcus, and 

 contains 2 — 4 vessels, originating from the vascular system 

 of the brood-capsule. When the Echinococcus-he&ds are deve- 

 loped in the interior of the process which has become converted 

 into a vesicle, which always takes place uniformly, the brood- 

 capsule bursts, and its walls, and with them the inner layer with 

 the individual heads, turn inside out. Lastly, the groups of 

 Echinococci, which ofteu swim about freelv in the Echinococcus- 

 sac, detach themselves, and the individual scolices fall separately 

 into this sac, where they die, whilst new generations are produced. 

 Moreover, the histological structure both of the mother-vesicle 

 and of the daughter-vesicles (vide infra) shows that the formation 

 of the heads never takes place on the outer wall (Huxley), but 

 on the inner one. Up to this period the process of formation is 

 the same in both species of Echinococcus ; but now a new 

 mode of generation makes its appearance. This consists in 

 the production of the so-called daughter-vesicles, which are 

 vesicles swimming about freely in the fluid of the Echinococcus, 

 and which exactly resemble the mother-vesicle in their structure 

 and in their proliferaut activity. Their mode of production is 



