278 



ZOOLOGY 



SECT. 



the best known instance of multiple production of scolices in a 

 cysticercus is Tcenia echinococcus well known as cause of the 

 disease termed Tiydatids, common in Man and in various domestic 

 animals. In this case the hooked embryo develops into a large 

 mother-cyst, from the interior of which daughter-cysts are budded off 

 (Fig. 22'?). Eventually from the walls of these daughter-cysts 

 there are formed numerous tape-worm heads, 

 or scolices (Figs. 228 and 229), which, when 

 fully formed, assume the appearance of 

 cysticercoids without the caudal vesicle. 

 These are readily detached, and should the 

 organ in which the cyst has been developed 

 be devoured by a Dog which is the final 

 host of the parasite some of these scolices 

 become attached to the wall of the intestine 

 and develop into the adult Tcenia echinococcus 

 which are very small as compared with 

 the size of the cyst and as compared with 

 other tape-worms. The eggs, passing out 

 with the faeces of the Dog, may be taken 

 into the digestive canal of Man or of one of 

 the domestic animals, and the minute em- 

 bryos escaping, reach some organ, such as the 

 liver or lung, in which they are capable of de- 

 veloping into a comparatively enormous cyst. 

 Asexual reproduction also occurs in < 

 une Platyhelminthes. In some Rhabdoccele 

 Turbellaria (Microstomum) a process of bud- 

 ding (Fig. 230) results in the formation of 

 strings of sexual individuals which may 

 eventually separate ; the new bud is always 

 formed from the posterior end of the last 

 FIG. 23p. Process of budding individual of the string. 



~Tey 'e-s c pot;' ^ The sporocyst stage in the Trematodes may, 

 von m Graff") dfeBdy mentioned, multiply by budding or 

 fission. The formation of new proglottides 

 in the Tape-worm may be looked upon either simply as growth 

 accompanied by segmentation, or as asexual multiplication, accord- 

 ing as we regard the proglottides as segments of a simple animal 

 or as zooids of a colony. There is this essential difference between 

 the formation of proglottides and the asexual multiplication by 

 budding in Microstomum, that in the former case the proglottides, 

 when they have been formed by segmentation of the undivided 

 part behind the head, do not in turn give rise by budding to new 

 proglottides. Spontaneous transverse fission has been observed 

 in certain Tricladida, and is often followed by the regeneration of 

 the lost portion. 



