DISTOiMUM CIRRIGERUM. 277 



General Anatomy of the Sexual Foem D. cireigeeum. 



The Non-Eucysted Animal. — The majority of the 

 animals were encysted in the muscles, but some few were 

 quite free, lying among the organs of the body. I am unable 

 to state for certain whether these were naturally free, for it 

 is quite possible that exposure to the water after the student 

 had opened the crayfish induced some of the animals to break 

 out of their cyst. One individual was fixed in the act of 

 escaping (Fig. IV). 



Some of the free animals were quite small, and were far 

 from being sexually mature, although fundaments of genital 

 organs could be seen ; while others were of full size, and had 

 ripe eggs in the uterus. Free individuals sexually mature 

 varied in length from about 1 mm. to about 1'75 mm., and in 

 breadth from '50 to '75 mm. The anterior and posterior 

 suckers are approximately equal in size, and are of very 

 considerable dimensions, having a diameter nearly half the 

 breadth of the body. Behind the posterior sucker the body 

 is cylindrical, while in front it is laterally compressed, and 

 tapers somewhat towards the anterior sucker. The genital 

 depression lies immediately in front of the posterior sucker, 

 and through it the cirrus is evaginated, while on the posterior 

 border of the depression is the crescentic opening of the 

 vagina. Terminally the excretory pore is visible, and on the 

 dorsal surface, a little posterior to the middle of the body, is 

 the extremely small opening of Laurer's canal, which is not 

 visible in the whole specimen (Figs. I, II, III). 



The general surface of the body is roughened by small 

 cuticular scales, which are variable in their amount of deve- 

 lopment in different individuals. They tend to be but 

 slightly developed in the middle region of the body, but are 

 more conspicuous at the two ends, especially the posterior 

 end. The scales are conical or plate-like elevations of the 

 general cuticle ; separate spinelets embedded in the cuticle, 

 as described in some Distoraids, could not be distinguished in 

 the adult, but in the developing animal they are quite obvious 



