PLATHELMINTHES 



201 



^^H several parthenogenetically reproducing generations of larval forms have 

 ^^f 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 ioxxa—Amphilina 

 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 Bud.), 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 present. 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 referred to free-living, Tutbellarian-like Plathelminthes, 

 which adapted themselves to a parasitic life. 



Literature. 



I. TCEBELLARIA. 



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



Nat. Hist. New York. Vol. iii. 1867. 



2. Chun, C. Die Verwandtschaftsbeziehungen zwischen Wiirmern 



und Colenteraten. Biol. Centralhl. Bd. ii. 1882—1883. 



3. GoETTE, A. Untersuchungen zur Entwicklungsgeschichte der 



Wiirmer. Leipzig. 1882 and 1884. 



4. GoETTE, A. Zur Entwicklungsgeschichte der marinen Dendrocolen 



Zool. Anzeiger. Jalirg. v. 1882. 



5. Graff, L. von. Monographic der Turbellarien. I. Rhabdoccelida. 



Leipzig. 1882. 



6. Hallez, p. Contributions a I'histoire naturelle des Turbellaries, 



Travaux Inst. Zool. Lille. Fasc. ii. 1879. 



7. Hallez, P. Embryogenie des dendrocoeles d'eau douce. Paris 



1887. 



8. IijiMA, I. Untersuchungen iiber den Bau und die Entwicklungs 



geschichte der Siisswasserdendrocolen (Tricladen). Zeitschr 

 iciss. Zool. Bd. xl. 1884. 



9. Keferstein, W. Beitrage zur Anatomie und Entwicklungsge 



schichte einiger Seeplanarien von St. Malo. Abhl. Gesellsch. Wiss 

 Gottingen. Bd. xiv. 1868. 

 10. KoROTNEFF, A. Ctcnoplaua Kowalevskii. Zeitschr. wiss. Zool 

 Bd. xliii. 1886. 



