OCCURRENCE OF TRICLADIDA 



is at once the largest and rarest. Planaria alpina (Fig. 14, B) 

 C D F 



Fia. 14. Forms of Triclads, with the distinguishing specific characters of certain 

 British forms. A, Planaria lactea 0. F. M., x 2 ; B, Plawiria alpina Dana, x 4 

 (after Kennel) ; C, I'luigocata gracilis Leidy (after Wood worth), x 6 ; C', the same 

 with the pharynges (ph) extmded ; D, (f mida ulvae Oer.,x4; E, Plaiiaria 

 ijmiocephala Dug. (after Schmidt), x 4 ; F, genitalia of Guiuia ulvae (after Wendt) : 

 O, head of Polycelis cornuta Schm. ; H, head of Polycelis nigra Ehr. ; I, head of 

 Planaria palyrhroa Schm. K to N show the distinctive characters of the genital 

 ducts in K, Polycelis nigra ; L, Planaria pulychnm ; M, Planaria alpina ; N, 

 J'lanaria tivrra Schultze (after lijima and v. Kennel). </, Genital atrium ; go, 

 common genital opening ; mar, ' ' muscnlo - glandular organ " ; wo, ' ' mouth " ; 

 iml, oviduct ; pe, penis ; ph, pharynx ; pyt; pyriform organs of unknown signifi- 

 cance ; ,vc, sucker ; up, sjiermatoiihore lying in (lit) uterus ; vd, vesicula semiualis. 

 (All except C and E are found in England.) 



is characteristic of cold mountain streams, but occurs down to 



