PLATHELMINTHES 201 



several parthenogenetically reproducing generations of larval forms have 

 been interpolated into the life-cycle. The close relationship of the 

 Trematodes and Cestodes is supported not only by their anatomical and 

 embryological agreement, but also by the existence of a form — Ampldlina 

 foliacea — which in its external shape more nearly resembles the Trema- 

 odes and was formerly reckoned among them (under the name of Mono- 

 stomum foliaceum Rtid.), but which, owing to the absence of an intes- 

 tinal canal and on account of the structure of the genital organs, must 

 be placed among the Cestodes (G. Wagener, No. 15). Its body is of a 

 leaf-like form, and there is only a single sexual apparatus i^resent. The 

 embryonic development takes place as in the Trematodes and Cestodes 

 (Salensky, No. 11). The egg is composed of an egg-cell and yolk-cells. 

 An embryonal membrane is formed, which the embryo breaks through. 

 This is armed with ten hooks, similar to those of the tapeworm 

 embryos. 



As regards the derivation of the Trematodes, they are to 

 be refei'red to free-living, Turbellarian-like Plathelminthes, 

 which adapted themselves to a parasitic life. 



Literature. 



I. TUKBELLARIA. 



1. Agassiz, A. On the Young Stages of a Few Annelids. Ann. Lyceum 



Nat. Hist. Neic York. Vol. iii. 1867. 



2. Chun, C. Die Verwandtschaftsbeziehungen zwischen Würmern 



und Cölenteraten. Biol. Centralbl. Bd. ii. 1882—1883. 



3. GoETTE, A. Untersuchungen zur Entwicklungsgeschichte der 



Würmer. Leipzig. 1882 and 1884. 



4. GoETTB, A. Zur Entwicklungsgeschichte der marinen Dendrocölen. 



Zool. Anzeiger. Jahrg. v. 1882. 



5. Gkaff, L. von. Monographie der Turbellarien. I. ßhabdocoelida. 



Leipzig. 1882. 



6. Hallez, P. Contributions ä l'histoire naturelle des Turbellaries. 



Travaux Inst. Zool. Lille. Fase. ii. 1879. 



7. HaIiLez, P. Embryogenie des dendrocceles d'eau douce. Paris. 



1887. 



8. Iiji-ma, I. Untersuchungen über den Bau und die Entwicklungs- 



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 wiss. Zool. Bd. xl. 1884. 



9. Keferstein, W. Beiträge zur Anatomie und Entwicklungsge- 



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 Bd. xliii. 1886. 



