THE TURBELLAR1A 



sixteen 

 another 



zooids (Fig. IX.), which will , ultimately separate from one 

 and proceed to live an independent life, reproducing in 

 the same way till some change in temperature or 

 food supply intervenes; then the genital organs 

 appear, and sexual reproduction takes place (see 

 61, 60, and 38) It is generally stated thatlftcro- 

 stoma differs from other Turbellaria in being 

 unisexual, but such is not the case ; it is a 

 protandrous hermaphrodite. 



FIG. IX. 



ORDER 2. Tricladida. 



Turbellaria, in which the intestine consists of three 

 main branches : one median anteriorly directed, and a 

 pair of posteriorly directed lobes, each of which gives 

 off a series of caeca. The mouth is post- central ; the- 

 pharynx tubular ; there is a single genital pore common 

 to the two sexes (monogonoporous). For an account of 

 the anatomy see 7, 34, and 41. 



There are nine families, which Hallez (31) arranges 

 in three tribes : 



TRIBE 1. MARICOLA. Marine Triclads, with in- 

 testinal caeca only slightly branched ; body depressed ; 

 uterus usually behind the genital pore. 



FIG. IX. 



Microstoma lineare, Oerst., undergoing division (from v. Graff). The 

 individual has first divided into two, near its middle, and each of these has 

 again divided. Each of the four zooids has again divided into two, and so- 

 on, till sixteen individuals are here marked out. TO, mouth of original 

 animal ; m', mouth of the hinder of the two individuals into which it- 

 divided ; in", the two mouths of the third generation ; m'", the four 

 mouths of the fourth generation ; the eight individuals of the fifth 

 generation have not yet acquired mouths, c, ciliated pits ; e, eye-spots ; 

 i, intestine. 



FAMILY 1. OTOPLANIDAE, with a pair of ciliated pits and a median 

 otocyst. Otoplana, du Plessis. FAMILY 2. PROCEROTIDAE, with otocyst r 

 but no ciliated pits. Cercyra, Schm. ; Fovia, Stimpson ; Gunda, 0. 

 Schm. (see Lang, 41) : Uteriporus, Bergendal ; Micropharynx, Jagersk. r 

 011 Earn batis. FAMILY 3. BDELLURIDAE, with a caudal fixing apparatus r 

 developed in relation to their parasitic habits. There are no rhabdites ; 

 two independent uteri or spermathecae, each with an independent pore, 

 Bdellura, Leidy ; Syncoelidium, Wheeler ; both occur fixed to gill hooks 

 of Limulus, on which they deposit their egg capsules (see 63). 



TRIBE 2. PALUDICOLA. Fluviatile forms, in which the intestinal caeca 

 are usually much branched ; the uterus lies between pharynx and penis. 



FAMILY 4. PLANARIIDAE. Planaria, 0. F. M. ; Dendrocoelum, Oerst. ; 

 Euplanaria, Hesse ; Dicotylus,-Griibe (27), (Fig. X. 5) ; Anocelis, Stimps. ; 

 Oligocelis, Stimps. ; Polycelis, Hemp, and Clap. ; Phagocata, Leidy (Fig, 

 XI. 2, see 65). 



TRIBE 3. TERRICOLA. Terrestrial forms, in which the intestinal caeca 

 are merely lobed ; mouth variable in position; form of body variable ; 



