THE FREE-LIVING FLATWORMS (TURBELLARIA) 



357 



92 (93) Angle of head 50° to 60°. Color a very dark sepia-brown almost 

 black by reflected light. . . Planaria agilis Stringer 1909. 



Length of immature worms usually not over 18 mm. Mature specimens collected have meas- 

 ured 30 mm. Well fed specimens in aquaria have attained a length of 55 mm. Color usually 

 very uniform. ^ Ventral surface but little lighter than dorsal. One variety found only in one 

 locality and with uniformly colored specimens, shows sharply defined non-pigmented spots. 

 Under lens a clear light-brown ground with fine dark brown, almost bkck pigment granules, 

 either quite uniformly distributed or arranged so as to give the appearance of a very close net 

 work. Circum-ocular spaces either oval or sUghtly pointed at outer anterior region and placed 

 just in front of or in line with the anterior margins of cephalic appendages. Some with light 

 areas on posterior margins of cephalic appendages, others with auricles uniformly pigmented. 

 A light median streak sometimes present. Lateral margin of head with a distinct inward curve 



just back of tip, also at junction of head with cephalic 

 appendages. Wider just in front of appendages than 

 at any point posterior to them except in large specimens 

 which are of about same width through pharyngeal region. 

 Mature specimens much broader proportionally than 

 immature. Asexual reproduction the usual method of 

 propagation in most localities. Very restless and active. 

 Collected from small ponds and spring-fed brooks either 

 among algae or on sandy bottom and often where water 

 flows swiftly. Neb., Mo., S. Dak., Wis., and Cal. 



Fig. 632. Planaria agilis. (A) Immature specimen from life. 

 X8. {B) Sexual organs, dorsal view: m, uterus: m^ uterus tube; 

 0, oviduct; gp, genital pore; a, atrium; sv, seminal vesicle; vd, 

 vas deferens: pi, cirrus lumen; la, limit of atrium. Much en- 

 larged. (After Stringer.) 



93 (92) Angle of head about 45°. 



Color reddish to yellowish-brown. 

 Planaria dorotocephala Woodworth 1897. 



Length of immature specimens 13 mm. Head about one-sixth of total length of body. Uni- 

 formly colored. Posterior margins of auricular appendages free from pigment. Sometimes a 

 narrow Ught median streak. Pigment in spots or patches, not a network or evenly distributed 

 as in P. agilis; ventral side much lighter than dorsal. Eyes just anterior to plane joining 

 auricles. Intestine usually with accessory posterior intestinal trunks which arise either at the 

 root of the pharynx like the two normal posterior trunks or exist as parallel branches of the 

 latter. Those of a side usually unite with each other near their posterior terminations. Very 

 active and restless. Sexual organs have not been described. III., Mich. 



Fig. 633. Planaria dorotocephala from life. X 7. (After Woodworth.) 



94 (85) Anterior end clearly not pointed 95 



95 (100) Anterior end truncated , 96 



96 (99) Margin of anterior end with a median anterior and two lateral 



rounded projections giving a sinuous outline 97 



