Loxogenes arcanum Nickerson. 275 



over them somewhat slowly and gradually but constantly. The mo- 

 vements however seem to be a coordinate series well adapted to 

 produce locomotion in a somewhat thick pasty medium, such a me- 

 dium as would be encountered in the small intestine of a frog. In 

 the few cases which have come under my notice no movements of 

 adhesion and no righting- movements were seen. 



III. Anatomical organization. 



a) External Features. 



Views of the ventral and dorsal surfaces of a preserved specimen 

 of L. arcanum are given in Figs. 2 and 3. These views show a 

 decided asymmetry the oral sucker being pushed considerably away 

 from the median plane toward the right side of the animal. A 

 similar disturbance of sj^mmetry is seen in Nickeeson's figure. The 

 right side of the body is thus shorter than its left side. As this 

 asymmetry is not found in the living animal, it must be an artifact 

 produced by the fixation reagents or the alcohols. It is readily 

 understood when one recalls the fact (Osboen, 1900, fig. 4) that, 

 the large and thick walled ejaculatory duct and vagina, which occupy 

 the left side of the body, ai-e not counterbalanced by similai" organs 

 on the right side. An examination of Figs. 2 and 3 will show that 

 the posterior end of the body is symmetrical. A line passing through 

 the ventral sucker and excretory pore divides the body approximately 

 equally but anteriorly it does not pass through the oral sucker. The 

 oral sucker lies considerably to the left of this line and it passes 

 not far from the genital pore. 



The outer surface of the body is covered everywhere with 

 large spines. They are very conspicuous in longitudinal sections 

 (see Figs. 12 — 16), where they are very deeply stained by the iron- 

 haematoxylin, in contrast with the cuticula which remains unstained. 

 The spines are broad and heavy at base where they have a thick- 

 ness of 0,0057 mm, and slope regularly to a bluntly pointed tip, 

 which is usually somewhat in-curved and often (Fig. 12) decidedly 

 hooked. The length of the spines ranges between 0,02 and 0,03 mm. 

 They are much longer than the thickness of the cuticula which 

 averages 0,01 mm, but are placed so obliquely that they barely 

 project beyond the surface. 



The oral and ventral suckers are both small and inconspicuous. 



