INTERNAL ANATOMY OF THE GAMASIN.E. 289 



the sexes show differences in this respect. 3. The form of the epigynum (or external 

 genital plate) of the female. 4. The number, form, and distribution of the other 

 chitinous plates of the ventral surface in both sexes. 5. The shape of the epistome (the 

 " Randfigur " of Kramer). 



Of these numbers 1 and 2 are, I believe, perfectly reliable ; number 2 is extra- 

 ordinarily different in different species, and is often most strange and characteristic in 

 form. Numbers 3 and 4, according to late classifications, are more generic than specific 

 differentiations. Number 5, the epistome, is a more doubtful question, and one not 

 fully settled. Dr. Kramer (supra, p. 283, note t) and Prof. Canestrini * were, I think, 

 of opinion that it was a reliable character. Megnin said that the epistome was not useful 

 in distinguishing species because it was variable, and was different both in the two sexes 

 and in different individuals of the same sex ; Kramer replied that it did not vary so 

 widely as to impair its value as a guide to species. My own opinion is that although 

 it is usually similar in the two sexes, yet it sometimes is markedly different — e. g. 

 Gamasus terribilis, G. crassus ; and also that, although the general characters are usually 

 alike in specimens of the same sex of the identical species, the details and exact form of 

 the organ vary considerably in different individuals, e. g. Hcemogamasus hirsutus (see 

 PI. XXXII. figs. 10, 11) ; and that, consequently, the epistome is useful in identifying 

 species, but only to a limited extent. It should, I think, always be figured ; but too 

 much reliance should not be placed on it ; it is only an aid, and where it is known to 

 vary as a secondary sexual character the sex from which it is drawn should be stated. 



The Male Genital System. 



The first departure from Winkler's type which I will mention is the male genital 

 system of Gamasus terribilis. I do not for a moment suppose that the form found in 

 that species is confined to it alone, but I select it as an excellent example, and one which 

 I am exceedingly familiar with. 



According to Winkler's description and figure (his fig. 18) (the latter stated to be 

 " schematisch ") of the sexual organs of Gamasus crassipes, they consist of — 1, a single, 

 azygous, globular testis with a trifling swelling on the hinder side, which he considers to 

 be the true spermatoblastic region (Keimlager) ; 2, two paired vasa deferentia, the length 

 of which is about five diameters of the testis, while their own diameter is not above 

 one seventh that of the testis — thus they are long and thin ; they arise quite sharply 

 from the testis, preserve an almost even diameter throughout, and terminate in 3, an 

 azygous ductus ejaculatorius (Ausfuhrungsgang) of about the same diameter as the vasa 

 deferentia and about one fifth the length ; 1, a large azygous accessory gland lying 

 between and underneath the vasa deferentia and entering the ductus ejaculatorius close 

 to where it springs from the vasa deferentia. This description I believe to be absolutely 

 correct ; I have carefully dissected Winkler's species and agree with him in all respects. 



* " Osservazioni intorno al genere Gamasus," Atti d. R. 1st. Yen. di Sci. &c. (1881). " Nuove specie del genere 

 Oamasus," ibid. 1881. ' I Gatnasi italiani,' Padua, 1882. 



SECOND SERIES. — ZOOLOGY, VOL. V. 43 



