282 ANIMAL PAEASTTES. 



vided with a spine formed the envelopes of the embryos in the 

 act of migrating out of the human body, and that this structure 

 in the oviduct had only passed through its metamorphosis at an 

 abnormally early period. Finally, Bilharz expresses the opinion 

 that these capsules cannot be destined to protect the embryos in 

 their outward migration, as they, (but never true eggs,) were 

 found in many places in the tissue of the mucous membrane, 

 and that they remain fixed in the tissue and become calcified, 

 just like the empty shells of the true eggs. If we combine all 

 this, we see at once that Bilharz* is not in a position to explain 

 the signification and importance of these structures. We shall 

 not be any more successful. The only thing which might, 

 perhaps, give us data for an explanation, is a comparative 

 glance at the class Infusoria. That the embryos of the Tre- 

 matoda, and especially those of our Distomum, resemble Infusoria 

 is well known. That the Infusoria are not only subject to a 

 change of skin (Ehrenberg), but also to a simple encysting process, 

 is known to us from the works of Stein and Cienkowsky, only to 

 mention one or two; and we even know from Guanzati that such 

 an encysting process is necessary in certain kinds of Infusoria, if 

 they are to retain the faculty of returning to life after drying 

 upon being moistened with water, or of supporting a high degree 

 of cold. These circumstances are, at all events, adapted to make 

 us think, that as no change of skin is in question, no pupa-case 

 can be spoken of, but that these spinous capsules are the cases 

 of the embryos of Distomum formed by themselves, within which, 

 like the six-hooped cestode embryos in the cysts formed by 

 their host, they pass to a higher grade of development, and at 

 the same time increase in size, as we see from Griesinger's 

 figures. Unfortunately, however, we have now got to the end 

 of our knowledge of the history of the development of our 

 Distomum, and the question remains whether the mature Dis- 

 toma are at last formed by the intervention of an outward 

 migration, with or without an intermediate step analogous to 

 the Cercaria, notwithstanding the continuance of Griesinger's 

 last stage in the body. 



Action of D. ha3matobium upon man, according to Griesinger. 

 This parasite is extraordinarily abundant in Egypt, for in 363 

 dissections its occurrence is noted 117 times by Griesinger, 

 and he even thinks that the lower stages may have been over- 

 looked. 



