17 



with fine granules, and a subcentral colourless, transparent' 

 structureless body, which, if the whole animalcule were 

 compared to a ciliated single-celled animal, would stand in 

 the relation of a nucleus to such cell. But this nucleus 

 has a very definite form : it is elongated, pointed at one 

 end, obtuse at the other end, on each side of which stands 

 out a short thick process. The ciliated integument of the 

 animalcule, after a brief course, ruptures, decomposes, and 

 sets free the body we have compared to the nucleus. This 

 body then increases in size, manifests a smooth non-ciliated 

 skin, and begins to show an extremely fine granular struc- 

 ture, but no other organ. Siebold, however, who could 

 not but recognize it as an independent individual organism, 

 asks if it might be a parasite of the infusorial-like embryo 

 of the Moriostoma, but observes that the constancy of its 

 existence in such w r as opposed to that idea, and he points 

 out its resemblance to the parents of certain Cercarice de- 

 scribed by Bojanus and V. Baer. The solitary progeny of 

 the ciliated embryo of the trematode Entozoon is closely 

 similar in form and structure to those gregariniform animal- 

 cules, since described and figured by Steenstrup*, in which 

 are developed the numerous cercariform individuals that he 

 saw ultimately metamorphosed into trematode Entozoa. 



The testimony of different good and independent wit- 

 nesses at different periods to different stages of the succes- 

 sive generations, which, when compared with one another, 

 are seen to link together and complete the metagenetic 

 cycle, is perhaps the best foundation for scientific confi- 

 dence in the truly marvellous result. 



Siebold t observes the development and birth of the cili- 

 ated monadiform embryo from the egg of the viviparous 

 trematode Entozoon, and the escape of the gregariniform 

 non-ciliated worm from the ciliated one. 



* ' On the Alternation of Generations/ Ray Society's Translation, 

 8vo, 1845, tab. 2. figs. 2 a d. 



f Wiegmann's Archiv fur Naturgeschichte, 1835, Bd. i. p. 67. 



B 



