354 



FRESH-WATER BIOLOGY 



77 (2) Pharynx either variable or cylindrical and lying within a pharyngeal 



pocket. Connective tissue well developed. 



Suborder Alloeocoela. 



The intestine is an irregular sac mostly with side lobes and an anterior and posterior branch. 

 It divides to form a ring in the median ventral region, thus enclosing the slender cylindrical 

 pharynx which is similar in position and appearance to that of the planarians. 



No fresh-water representative of this Suborder has been definitely established for this 

 country. It seems clear that some must exist in this region and be found on further study of 

 the American fauna. 



78 (i) Intestine consists of three main branches, one an anterior branch 



median in position, and two running to the posterior end of 

 the body, one on either side of the pharyngeal region. 



Order Tricladida . . 79 



Mostly larger than in the preceding order. Pharynx usually median ventral in position, elon- 

 gated, cylindrical, and lying within a pharyngeal pocket with the free end directed posteriorly. 

 Compare figures of a typical Triclad (Fig. 590) and Rhabdocoel given on page 333. 



79 (104) Found in fresh-water ponds or streams. . . Suborder Paludicola. 



Only one family PLANARIIDAE . . 80 



Body elongated, flattened, often with conspicuous cephalic appendages. Inconspicuously 

 colored. 



80 (103) Pharynx one 81 



8 1 (82) With an adhesive disk on anterior end Dendrocoelum. 



Only one species known in this country. 



Dendrocoelum lacteum Oersted 1844. 



Greatest length 22 mm., breadth 2 to 3 mm. 

 Color milk-white, creamy, yellowish, or in 

 larger older specimens sometimes roseate. No 

 pigment except in eye spots. Very translu- 

 cent. Intestine colored by contained food. A 

 slight constriction just behind the plane of the 

 eyes sets off the head and produces the rounded, 

 cephalic appendages. Posterior end rounded. 

 Lateral margins nearly parallel when at rest 

 or contracted. Median adhesive disk extremely 

 variable. Usually about one-third of the broad- 

 est diameter of the head. Inconspicuous in 

 small specimens. It is not a true sucker but 

 consists of a depression into which the glands 

 open and with the margin somewhat raised. 

 Two eyes normally but from one to six accessory 

 eyes are common. Mass., Mich., Penn., Wis. 



What is probably a variety of this species is 

 described as a non-pigmented eyeless Dendro- 

 coelum collected from Mammoth Cave and ad- 

 joining caves in Kentucky. 



FIG. 628. Dendrocoelum lacteum. (A) From life. X4. 

 (B) Sex organs, dorsal view: brs, copulatory bursa; 

 dt ej, ductus ejaculatorius; gl sh, shell gland; gl prst, 

 prostate gland; go po, genital pore; ov dt, oviduct; 

 brs. pe, cirrus; ut, uterus; va df, vas deferens; vag, va- 



gina. X 14. (After Woodworth.) 



ffl- pr'st. 



82 (81) Without an adhesive disk on anterior end 83 



