82 



PLANARIANS 



Sub-order A. Rhahdocoelida. — Of small size ; body cylin- 

 drical or depressed ; without an intestine, or with a simple 

 unbranched intestine; the female genital glands always 

 compact, not follicular ; genital apertures single or distinct. 



Tribe I. Acoela (fig. 1, a). — "With a digestive paren- 

 chyma not differentiated into intestine and parenchyma 

 proper; with no nervous system or excretory organs; 

 sexual organs hermaphrodite, with follicular testes and 

 paired ovaries ; generally without a pharynx, but having 

 otoliths; all the forms marine. Many quite flat, with 

 the lateral margins bent down towards the ventral surface 

 {Convoluta), frequently with brown or green parasitic algae 

 in the parenchyma. 



Tribe II. Rhabdocoela (fig. 1, 6). — Intestinal tract and 

 parenchyma separate; nervous system and excretory 

 organs present ; with compact testes and female genera- 

 tive glands (ovaries or separated germarium and yelk 

 glands) ; with a complicated pharynx, but generally without 

 otoliths. Numerous forms, freshwater and marine ; the 

 genus Prorhynchus (two species) also in damp earth. The 

 Microstomida (fig. 9) propagate asexually. Freshwater 

 forms mostly belopg to the families Mesostomida and 

 Vorticida, some of which contain green parasitic algae. 

 Marine forms include representatives of these two families 

 and of the Proboscida (with a tactile proboscis). Of the 

 family Vorticida, the genera Graffilla and Anoplodium are 

 parasitic, the former in Gastropods the latter in Echino- 

 derms (Holothurians). 



Tribe III. Alloiocoda (fig. 1, c). — Intestinal tract and 

 parenchyma separate ; nervous system and excretory 

 organs present ; with follicular testes and compact female 

 glands (as in the Rhabdocoela); pharynx similarly 

 developed as a shorter or longer sac. One family {Mono- 

 tida), with otoliths. All the species marine, with one 

 exception, Plagiostoma lemani, which lives in the deep 

 water of the Alpine lakes. 



Sub-order B. Dendrocoelida. — ^Large forms, with a 

 flattened body, branched intestine, follicular testes and 

 follicular yelk glands or ovaries ; without otoliths. 



Tribe I. Tricladida. — Body elongate ; intestine with 

 three main branches uniting to open into a cylindrical 

 retractile pharynx; with follicular testes, two round 

 germariums, and numerous yelk follicles, with a single 

 sexual aperture. Planaria, Dendrocoelwm, Polycelis (fig. 

 1, g) are inhabitants of fresh water (with great power of 

 reproduction). Terrestrial forms (fig. 1, e,f) of leech-like 

 shape, especially met with in the tropics (only two 

 European species Rhynchodemus terrestris and Geodesmus 

 hilineatus) ; marine forms Gunda (characterized by a 

 metameric structure), Bdelloura (external parasite of 

 Limidtis). 



Tribe II. Polycladida (fig. 1, d). — Body leaf-like, thin, 

 and broad, with numerous branched or retiform intestinal 

 coeca which unite to form a central tube (stomach) ; with 

 follicular testes and follicular ovaries, with two separated 

 genital apertures, the male in front of the female ; without 

 {Acotylea) or with (Gotylea) a sucker situated behind the 

 female generative opening. All marine. 



Literature. — The most recent works, which also contain a full 

 account of what has gone before, are the following : — Rhabdocmla. — 

 L. V. Graff, Monographie der Turhellarien : 1. Hhabdoccelida, Leip- 

 sic, 1882, with 20 plates. Marine and Freshwater Tricladida. — 

 A. Lang, "Der Ban von Giiwda segimentotound die Verwandtschaft 

 der Platyhelminthen mit Ccelenteraten und Hirudineen," in Mitth. 

 Zool. Stat. Neapel, vol. iii., 1881; El. Metschnikoff, "DieEni- 

 bryologie von Planaria polychroa," in Zeitschr. f. loiss. Zool., vol. 

 xxxviii., 1883 ; Isao Jijima, " Untersuchungen iiber den Ban nnd 

 die Entwickelungsgeschichte der Siisswasser-Dendrocoelen," in 

 Zeitschr. f. wiss. Zool., vol. xl., 1884. Land Planarians. — H. N. 

 Moseley, "On the Anatomy and Histology of the Land Planarians 

 of Ceylon, with some Account of their Habits, and with a Descrif - 

 tiou of Two New Species, and with Notes on the Anatomy of somo 

 European Aquatic Species," in Phil. Trans. (London, 1874), and 

 "Notes on the Structure of several Forms of Land Planarians, 

 with a Description of Two New Genera and Several New Species, 

 and a List of all Species at present known," in Quart. Jour. Micr. 

 Sci., vol. xlvii., 1877 ; J. v. Kennel, "Die in Deutschland gefun- 

 denen Landplanarien Bhynchodemus terrestris und Cfeodesmus 

 bilineatus," in Arbeit. Zool.-Zootom. Instit. Wiirzburg, v., 1879. 

 Polycladida. — A. Lang, "Die Polyoladen," in Fauna und Flora 

 des Golfes von Neapel, No. 11, 39 plates, Leipsic, 1884-85. 



(L. V. G.) 



