THE CYSTIC ENTOZOA. 485 



from the animal becoming so distended, in consequence of 

 the increased size and number of the young within it, that it 

 bursts when the young are exposed, and the parent sac, which 

 is now useless, absorbed, the progeny in the meantime becom- 

 ing attached to the peritoneum.* The external membranes in 

 Diskostoma spread over the, as yet, uninfested portions of the 

 peritoneum, and give origin to a number of cells from the 

 attached surface, each of which, becoming parents, gradually 

 increases in size, from the addition of new matter within the 

 young cells. These young cells are the germs of the future 

 animals. The other mode of development, or that intended 

 for the formation of new groups, is similar in both animals. 

 The young or secondary cells, bursting from their formative 

 cell, by some means escape from the parent sac, and so gain a 

 situation at some distance from the original group, where they 

 become attached, in time throw off young cells, and thus be- 

 come the origin of a new set. 



Eelative to the mode of reproduction in these animals, it 

 is found that in Astoma, and the higher cystic entozoa, the 

 numbers proceeding from one parent may be unlimited, 

 whereas in Acephalocystis, generation ceases with the quater- 

 nary series of young, unless this series, or the gemmules of 

 some of the preceding, escape from the original sac and are 

 able to form a nidus in any portion of the liver, or other 

 organ yet uninfested. For it appears necessary to the exist- 

 ence of the common hydatid that it be completely enveloped 

 in the tissues of the infested being. To ensure this normal 

 habitat, then, the animal must escape during the period of its 

 gemmule existence from the parent ; but, as most generally 

 happens, if the parent hydatid be so deeply buried as not to 

 allow free rupture of its coats within a certain period, decom- 

 position ensues as already described, and so existence is 



* See Preparation in Mweum of Royal College of Surgeons, Edinburgh, 

 No. 2244. 



