THE FREE-LIVING FLATWORMS (TURBELLARIA) 



333 



KEY TO NORTH AMERICAN FRESH-WATER TURBELLARIA 



Including the Land Planarians 



I (78) Intestine a single blind tube, median in position. 



Order Rhabdocoelida . . 2 



The intestine consists of a simple rod-shaped or sac cavity which rarely has lateral diverticula 

 and never is divided into two distinct post-pharyngeal branches. Mostly small forms, never 

 more than a few millimeters in length. The following Sgures (Figs. 589 and 590) facilitate a 

 comparison of structure in the two great orders, Rhabdocoelida and Tricladida (p. 354). 



Fig. 589. Structure of a Rhabdocoel. 

 Dalyellia rossi. Compressed, ad, atrial 

 glands; he, bursa copulatrix; bsi, duct lead- 

 ing from bursa copulatrix; ch, chitinous 

 part of the male copulatory organ; da, in- 

 testine; dg, duct of yolk gland; ge, ovary; 

 go, genital pore; mgc, male genital canal; 

 mph. retractor muscles of pharynx; ph, 

 pharynx; pp, cirrus; pr, reddish reticu- 

 lar pigment; pz, yellow pigment cell; rs, 

 receptaculum seminis; sph, sphinctor 

 muscle of the uterus; te, testes; vd, vas de- 

 ferens; vs, seminal vesicle; vi, yolk gland; z, 

 esophageal cells; e, eye; u, uterus. X 

 SO. (After von Graff.) 



Fig. 590. Structure of a Triclad. 



Diagram of a Planarian. ag, 

 genital atrium; aw. eye; com, cross 

 commissures of nervous system; 

 d', anterior, and d" , pwsterior 

 branches of intestines; do, yolk 

 gland; ex, excretory canal; exp, ex- 

 cretory pore; gl, brain; gp, genital 

 pore; In, longitudinal nerve; m, 

 mouth; od, oviduct; od', common 

 oviduct; ov, ovary; p, cirrus; pk, 

 pharynx; pht, pharyngeal pocket; 

 te, testes; ui, uterus; utd, uterine 

 duct; vd, vas deferens. (After 

 Bohmig.) 



2 (77) Pharynx simple, cask-shaped or rosette-shaped. Connective tissue of 



body cavity poorly developed. 



Suborder Rhabdocoela . . 3 



The mesenchyma often consists of but a few strands of connective tissue and contains large 

 spaces filled with a perivisceral fluid. 



3 (30) Reproductive organs simple. Female organs consist of ovary only. 



Section Hysterophora . . 4 



These forms possess no accessory female organs, i.e., no separate yolk glands, uterus, female 

 copulatory apparatus, etc. Asexual reproduction among rhabdocoels is found only in this 

 section of the order. 



