142 ILLINOIS BIOLOGICAL MONOGRAPHS [i3 



and to be in many cases just covered by the posterior border of the segment 

 immediately ahead. It is in the form of a narrow tube, often somewhat 

 enlarged ventrally, with a length of from 85 to 115^t and extending at 

 right angles to the general surface of the strobila. A secondary genital 

 cloaca or ductus hermaphroditicus is present at the bottom of this tube and is 

 separated from the latter by a valve-hke muscular extension of its walls 

 (Fig. 88). Behind this the cirrus is often found partially extended and directed 

 backward towards the opening of the vagina or actually in contact with the 

 vaginal sphincter. No sphincter muscle surrounding the genital cloaca at 

 any level was found, altho a number of frontal fibres of the body muscles, 

 curving around the structure both ahead and behind have the general appear- 

 ance of such a structure. Very early traces of the reproductive rudiments 

 were found in sections of segments 75mm. from the tip of the scolex of one of 

 the largest strobilas studied. 



The testes, continuous from proglottis to proglottis, are spherical to ellip- 

 soidal in shape, with their longest axes usually transverse in the latter case. 

 The measurements from sections are as follows: width, 64 to 75/x; length, 45 

 to 60; depth, 64 to 80. On account of their being closely and irregularly crowd- 

 ed in the very short segments no attempt was made to count them directly; 

 but the average number in the transverse sections (22 to 23) multiplied by 

 the average for each proglottis from sagittal sections of a long series of seg- 

 ments (3 to 4) gave about 67. The correct number is probably between 60 

 and 70. They are arranged in a layer in the dorsal half of the m.edulla, where 

 they show some tendency towards stratification. A few, however, were found 

 outside of the medulla, that is beyond the inner frontal muscles and between 

 fasciculi of the main longitudinal musculature. 



The vas deferens forms a compact mass of coils, closely applied dorsolateral- 

 ly to the proximal deflected end of the cirrus-pouch, and alternating irregularly 

 from side to side constantly opposing the uterus-sac. In ripe proglottides it 

 is quite compressed anteroposteriorly by the uterine tube, and also, as 

 a consequence, often extends thruout almost the whole of the medulla 

 dorso ventrally, in which case it is crescentic in outline in transverse sections 

 with the concave side directed towards the median fine so as to somewhat sur- 

 round the cirrus-sac. The average measurements of the mass of coils are: 

 length, 0.085mm; width, 0.175; depth, 0.400. While it was found impossible 

 to measure satisfactorily the size of the duct, gorged with spenns in the mass, 

 it was seen to enter the base of the very muscular cirrus-sac with a diameter 

 of 7.5/i. Within the latter it expands to 15/1 and proceeds with this caliber 

 in the form of a compact lot of close and somewhat spiral coils for about one 

 quarter of the length of the pouch. In the second quarter, i.e., from the 

 ventral end of the sac, it pursues a straight course and evidently functions as 

 a quite efi&cient sperm receptacle since it is here usually from twice to three 

 times as large as before. In the dorsal half of the pouch it again dimishes to 

 from 5 to 7/x and continues still in a straight course to the opening as the cirrus 

 proper. Thruout its whole course its wall is very thin, including only a very 



