196 TAPEWORMS OF HARES AND RABBITS STILES. 



All of the specimens are so contracted that a study of the general 

 anatomy in detail is out of the question; enough can be given, however, 

 to clearly define the species from other members of this genus. Tak- 

 ing the type specimen as basis for description, I find the following 

 characters: 



The head measures 0.480 mm. broad by 0.32 mm. long. The rostellnm 

 measures 80 // in its trau verse and 48 JJL in its longitudinal diameter; 

 its equator is provided with a crown on other preparations shown to 

 be double of minute booklets 12 p long. It is impossible to count the 

 hooks, but there are about as many present as in I), salmoni i. e., about 

 90 to 120. The suckers are oblong and measure 0.2 to 0.224 inm. by 0.14 

 to 0.16 mm.; they are armed with numerous booklets arranged in rows. 

 An estimate of their number is even more difficult than in the case of 

 Davainea salmoni (see p. 198). There are about 75 diagonal rows of 

 roots; from 5 to 20 roots have been counted in different rows. Five 

 hundred to seven hundred hooks would probably not be a high esti- 

 mate for each sucker. The suckers appear at first sight with low pow- 

 ers, to open at right angles to the longitudinal surface of the worm, 

 but a careful study shows that the entire muscular bulb, together with 

 its numerous hooks, is retracted into a sac-like structure which opens 

 directly forward namely, at right angles to a transverse section; in 

 other words, the entire sucker is inverted in the parenchyma of the 

 head ; the direction of the opening of this invagination varies slightly 

 in different specimens. A circular canal 9 yu in diameter surrounds the 

 rostellurn; a longitudinal canal runs in the dorsal and another in the 

 ventral median line, which in all probability are connected with the cir- 

 cular canal, although this could not be absolutely demonstrated. 



The contraction was such that the neck and the commencement of 

 stabilization could not be judged satisfactorily, although the neck is 

 apparently short, segmentation beginning near the head. As nearly as 

 could be estimated, the strobila contains about 950 segments; in this 

 estimate about 300 segments are allowed for the first 10 mm. of the worm. 

 In the anterior portion, the four longitudinal canals are very distinct 

 and laterally the longitudinal nerve is indistinctly visible; the larger 

 (evidently ventral) canal is lateral of the smaller (dorsal) canal. About 

 1.12 mm. from the head a small deeply- staining line of cells develops in 

 the median line of the segments, running parallel to the anterior mar- 

 gin; this gradually increases in length as the segments are followed 

 distally: this is interpreted as the anlage of the genital canals and 

 probably also of the female glands. Very shortly after its appearance 

 two groups of testicles are noticed, one group each side of the median 

 line. The cirrus pouch and vagina appear in the lateral field, all of 

 the genital pores being unilateral in the anterior half of the segment. 

 The pouch is small, measuring 0.12 mm. long by 60 ^ broad; no clearly 

 defined vesicula seminalis could be seen, but the coils made by the 

 retracted cirrus appear to occupy the entire pouch; the vagina is 



