108 ILLINOIS BIOLOGICAL MONOGRAPHS [396 



ment eventually gets the upper hand and develops at the expense of the other. 

 This is borne out by the fact that in half the cases one rudiment was much 

 larger than the other. The above mentioned groups of rudiments were divided 

 and subdivided by less and less pronounced transverse furrows in the following 

 manner : 



67 82 101 



43 24 35 47 54 47 



24 19 10 14 14 21 18 13 16 16 14 12 12 20 12 15 



This continued until eventually the groups of four (or five, rarely six) sets 

 of genitaha of the authors could be made out. Each of these in turn was 

 seen to be divided into two groups of two sets each, so that each lateral crenu- 

 lation corresponded to two (or three) of them, i.e., to the l-32nd division de- 

 scribed above (Fig. 57). In ripe segments this arrangement may obtain or the 

 segment may divide again peripherally, so that each crenulation then corres- 

 ponds with one set of genitalia (Figs. 59 and 60). The latter figures show 

 that "complete" transverse furrows are present between every 8 or 9 (some- 

 times 7, or apparently even 3, 4, 5 or 6!) genital segments. However, other 

 more relaxed strobilas in alcohol showed complete furrows only every 16 to 17 

 sets of genital segments, there often being a group of 5 instead of the much 

 more common group of four — but in the same neighborhood of the strobila 

 just as complete grooves every 8, 9 or 10 sets. This shows that a grouping of 

 the genital segments into lots of approximately 16, as mentioned by Luhe 

 (1910:25) is so irregular that it can scarcely be said to occur "as a rule, " and 

 that the peculiar method of segmentation of the anterior end of the strobila 

 mentioned above (p. 102) is very difficult to follow with any degree of certainty 

 beyond the region of differentiation of the genital rudiments. 



The genital sinus is situated on a low papilla (Fig. 59) on the dorsal surface, 

 in the median Une and from one-half to two-thirds of the length of the genital 

 segment from its anterior border, while the uterine opening on the ventral sur- 

 face is located much farther forward, even at the bottom of the groove corres- 

 ponding to the indentation of the edge of the strobila, separating the crenula- 

 tions mentioned above. The sinus itself is circular in outUne and from 40 to 

 45m in diameter by 15 to 20ju in depth. At its bottom the cirrus and vagina 

 open close together, the latter immediately behind the former, thru a sec- 

 ondary sinus or ductus hermaphroditicus, the walls of which are often found 

 protruding thru the opening of the larger vestibule as if to form part of a func- 

 tional cirrus (Fig. 95). 



The testes are arranged in two lateral fields in the medullary parenchyma, 

 as pointed out by Lonnberg, and are continuous from segment to segment, altho 

 they show some tendency towards division interproglottidally. The number 

 was given by Matz (1892:106) as about 76, with their size as 40.8^, but here it 

 was found to be from 30 to 60, while their size was 35 to 70/^, 60 being the 



