INTEENAL ANATOMY OF THE GAMASIN.E. 289 



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

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

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

 " Randfigur '' of Kramer). 



Of these numbers 1 and 2 arc, I believe, perfectly reliable ; number 2 is exti*a- 

 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. Megniu said that the epistome was not useful 

 in distinguisliing species because it w^as 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 altliough 

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

 Gumasus terrib'dis, G. crassns ; 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 dilfereut individuals, e. g. Scemogamasus hirsntus (see 

 PL 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 fi'om which it is drawn should be stated. 



The Male Genital System. 



The first departure from Winkler's type which I will mention is tlie 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 exceedinsjlv 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, 

 azvaous, ""lobular testis with a triflins' swellina: on the hinder side, which he considers to 

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

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

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

 deferentia and about one fifth tlie lenii;th ; 1, a larire azv2:ous accessorv ti^land Ivinsj 

 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 alisolutely 

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



* " Osservazioni iutorno al genere Gamasii.''" Atti d. R. 1st. Ven. di Sci. &c. (1881). " Xuove specie del genere 

 Oamasiis" ibid. 1881. ' I Gamasi italiani,' Padua, 1882. 



SECOND SERIES. — ZOOLOGY, VOL. V. 43 



