THE VAGINA AND aTERUS AND THEIR OPENINGS. 



701 



The most important histological character of the vagina is the 

 presence of a muscular layer consisting, for the most part, of circular 

 fibres, which begins at the base of the vaginal 

 entrance, and acquires a specially strong de- 

 velopment in the dilated sac. The internal 

 lining of the canal is formed of a thin, but 

 sharply defined cuticle, which is continued at 

 the vaginal opening into the cuticular cover- 

 ing of the body. 



It was only after the discovery of this 

 vagina that it became possible to homologise 

 the structural relations of the reproductive 

 organs in Bothriocephalus with those of the 

 Tcenice. We know now that in the former as 

 well as in the latter the uterus serves only 

 for the reception of the ova, and the differ- 

 ence between it and the Tcenice is thus 

 essentially reduced to this, that the uterus is 

 not closed, but has an opening through which 

 the ova pass outwards. 



The Uterine Aperture, as has been already 

 described, is seen a short distance (Fig. 367) 

 behind the genital cloaca, at an interval of 

 between 0-25 and 0"4 mm., according to the 

 state of contraction of the segment. It is sur- 

 rounded by margins which are but little 

 swollen, has a width of 015 mm., and, 

 rapidly narrowing, leads into a canal (of 0'04 

 mm. in diameter) which is inserted at right 

 angles to the ventral surface, penetrates 

 the cortical layer, and then somewhat sud- 

 denly widens into the' upwardly directed first coil of the uterus 

 which lies right or left of the ciiThus-pouch. 



The Uterus, whose true structure was first recognised by Esch'richt, 

 consists of a simple coiled canal, which extends from behind forwards 

 in the internal layer of the joints, and at the height of its develop- 

 ment occupies the greater part of the whole median portion. The 

 windings>,extend alternately right and left across the middle line, and 

 the adjacent bands of their loops at first suggest the lateral processes, 

 which we have already seen in the large jointed Tcenice. On closer 

 examination, however, this resemblance is seen to be an illusion,^ and 



' Botticher's statement that a direct Connection exists in the middle line between the 

 loops which here cross each other is based on a misinterpretation. 



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Flo. 367. — Diagrammatic 

 representation of the course 

 and connections of the vagina, 

 as seen in longitudinal sec- 

 tion, v.d; vas deferens ; 

 c.p. , cirrhus - pouch ; v. 

 vagina; vt., uterus; ut.o., 

 uterine opening ; f.c, fertil- 

 ising canal ; o.d,, oviduct ; 

 s.g., sheU-gland. 



od. 



