66 CO. Whitmau 



ons , though not rare. One thing is observable in respect to these as- 

 sumed ueoplastic formati ons , that their number is constantly diminish- 

 ing. It has happened over and over again tbat nuclei claimed to be 

 neoplastic , bave turned out, on re-examination witb better raethods, or 

 w^itb greater care, to be notbing more tban ordinary endogenous nuclei. 

 This bas occurred so frequently , tbat it would now not be very rasb to 

 predici that another decade will completely exhaust the list. As to the 

 cases still remaining, it is very clear that the best evidence for them is 

 the wrant of evidence against them. Strasbürger (47, 48), who among 

 botanists, has given most attention to this subject, and who in bis ear- 

 lier writings maintained neoplastic nuclei to be of very general occur- 

 rence, now thinks that nothiug of the kind occurs in the vegetable king- 

 dom. Mark, who has recently reviewed this question, considers it 

 »extremely doubtful whether new nuclei arise in animai cells without 

 the least visible connection with the nuclear substance of preexisting 

 nuclei.« (45, p. 545.) 



Where the contrary has beeu asserted, as in the regeneration of 

 epithelium (28i, Gregarina gigantea (23 , ciliated spores of temete di- 

 visa (30) 1, infusorific germ-cells of Dicyemids, etc.. the negative results 

 must be attributed either to over-hasty examination, or to exceptional 

 difficulties in the way of obtaining reliable information. 



Chapter IV. 



Systematic Afflnities. 



Krohn and Erdl expressed no definite opinion ou the systematic 

 relations of the Dicyemids. In a review of the helminthological pro- 

 ductions of 1843 and 1844 (12), Siebold records bis opinion in the fol- 

 lo wing words. 



»Ref. möchte diese sonderbaren Wesen mit ihrem infusorienartigen 

 Inhalte für die schlauchartigen Larven eines dem Genera- 

 tionswechsel unterworfenen Thieres halten. Derselbe kann 

 dabei nicht umhin , auf die iihnlichkeit dieses infusorienartigen Inhalts 

 mit den räth sei haften, von Jon. Müller- beschriebenen ungeschwänz- 

 ten Psorospermen aufmerksaoi zu machen.« p. 247. 



The production of two kinds of embryos by Dicyema led Kölliker 



1 R. Hertwig (33) States that the nuclei of the spores are derivative. 



2 »Über eine eigenthümliche krankhafte parasitische Bildung mit specifisch 

 organisirten Samenkörperchen.« Müll. Arch. 1841, p. 477. 



