INTERNAL ANATOMY OF THE GAMASID^. 297 



The Female Genital System. 



It is in this group of structures that we find the widest variations iu the Gamasina3 ■ 

 we here not only have great differences in the same part in distinct species, but we also 

 meet with a whole set of organs in a large section of the family which are absent from 

 those hitherto described, and these new organs present considerable variety amongst 

 themselves. I will now proceed to describe them, but first for comparison I will 

 shortly take from Winkler's memoir the principal features of the organs as hitherto 

 known and described by him. 



The female genital system in Gamasus crassipes consists of the following parts, viz. : 



1. An almost globular ovary * fairly corresponding to the single globular testis of the 

 same species ; in this ovary the germinal portion is the central, and the more developed 

 eggs are found round the periphery in sacs, the walls of which are so fine as not always to 

 be readily seen. These sacs are temporary outpushings of the outer investing tunic of the 

 ovary, and may be called oocysts or ovicells. 2. A short unpaired nearly straight oviduct. 

 3. A larger continuation of the same, with more glandular walls, which Winkler calls the 

 uterus, and where he says the egg attains much of its development. 4. The vagina, which 

 is a largish chamber, open below, but with a domed recess above just over the opening, 

 which recess usually or frequently contains a ball of spermatozoa. 5. Two small 

 vaginal glands which open into the vagina just at the base of this domed recess. And 

 finally 6. The epigynum or external genital plate, which in this species is a large, 

 almost triangular, plate, with its straight edge backward, and is hinged by that edge to 

 the ventral surface ; it occupies most of the space between the two hind pairs of le°"s, 

 and entirely closes the genital aperture. Within this plate is a somewhat elaborate 

 structure of chitinous pieces, the precise function of which is not known. 



I will contrast with this the organs which I find in Hcemogamasus horridus. I select 

 this species as a type, and as that to be first described, because in it the organs which I 

 believe to be entirely undescribed are found in about their simplest form. 



It will be most convenient to commence in the reverse order from that used in regard 

 to G. crassipes. The epigynum (genital plate) in this species (fig. 2, epg), and indeed in 

 all species of the same genus which I have hitherto examined, is no longer a separate 

 plate working on a ginglymous hinge and closing the genital opening ; it is a plate, 

 truncated in front, firmly attached by its whole surface to the ventral cuticle ; precisely 

 like the other chitinous plates of the underside of the creature, or probably it would be 

 more correct to say that both it and the others are actually portions of the ventral 

 cuticle, only differing from the other portions by the deposition of chitin in the cells. 

 The genital opening is only a long, somewhat curved, slit placed in the flexible cuticle 

 between the epigynum and the sternal plate ; it is, however, somewhat protected by a 

 very delicate and narrow flexible border which runs along the anterior edge of the 

 epigynum. 



* I use the word ovary in this paper in the sense in which it is used by all writers on the Acarina, viz., as the 

 whole organ in which the eggs originate, and that solid part in which they are developed in oocysts (as above 

 defined) before they pass into the free and tubular oviduct. 



SECOND SERIES. — ZOOLOGY, VOL. V. 44 



