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 iorm—Amjihilina 

 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 Eud.), 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 dei-ivation of the Trematodes, they are to 

 be referred to free-living, Turbellarian-like Plathelminthes, 

 which adapted themselves to a parasitic life. 



Literature. 



I. TURBELLARIA. 



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. Centralbl. Bd. ii. 1882—1883. 



3. GoETTE, A. Untersuchungen zur Entwicklungsgeschichte der 



Wilrmer. Leipzig. 1882 and 1884. 



4. GoETTE, A. Zur Entwicklungsgeschichte der marinen Dendrocolen. 



Zool. Anzeiger. Jahrg. v. 1882. 



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



Leipzig. 1882. 



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



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



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



1887. 



8. IiJiJiA, I. Untersuchungen iiber den Bau und die Entwicklungs- 



geschichte der Siisswasserdendrocolen (Tricladen). Zeitschr. 

 tviss. 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. Ctcnoplana Kowalevskii. Zeitschr. wiss. Zool. 

 Bd. xliii. 1886. 



