16 STUDIES ON ACAEI. 



limbs. The above account of the supposed respiratory system is given 

 with great reserve. With the exception of Csokor, who seems to liave 

 seen the main tracheae, acarologists state that there is no respiratory 

 system in this group. 



The sexual openings, penis, etc. — The accounts of the genital organs 

 of Demodex given by the most eminent acarologists, are of a very 

 divergent nature. In his ' Prospetto dell' Acarofauna Italiana,' Cane- 

 strini frankly admits that he can only distinguish the females in which 

 developing ova are present, and he does not describe the males. Berlese 

 is of opinion ('Gli Insetti,' vol. ii. p. 37) that the genital and anal 

 orifices of the male Demodex are situated together at the posterior end 

 of the ventral surface of the abdomen. Neumann follows Megnin, and 

 states (' Parasites et Maladies Parasitaires du Chien,' etc., p. 58) that 

 the slit at the anterior end of the abdomen serves both for copulation 

 and the exit of the eggs, and is larger in the female than in the male. 

 He says there is a genital armature in front of this slit in the male sex. 

 Megnin says that the penis has the form of a conical tubercle, and 

 figures it as quite a short structure (see his fig. 1, pi. xxvi., ' Parasites 

 et Maladies Parasitaires '). Csokor uses the word " Knotschen " to 

 describe the male organ, — from which one would suppose he thought it 

 to be quite short and like a tubercle. In reality the males of Demodex 

 are easily distinguished by the presence of an elongated chitinous organ 

 of comparatively large size, situated internally, which is undoubtedly 

 the penis. It is a slender rod-like structure, attached by the heart- 

 shaped or rather bulb-shaped posterior end, which is usually trans- 

 versely striated, whilst the anterior end points forwards and upwards 

 towards the dorsal surface. I have been able to examine specimens of 

 D. folliculorum and of D. bovis which have the penis either partly or 

 wholly protruded (see fig. 15, PI. III. .& figs. 7, 8, PI. II.), and have also 

 dissected out this organ in the latter species. The penis usually consists 

 of two portions or branches, one of which ends in a very fine and delicate 

 point ; the other is more blade-like, being wider and having one edge 

 rather strongly chitinised — it is not so finely pointed as the other half, 

 and possibly serves as its sheath or protective guard. The penis seems to 

 be contained in a special internal pocket or pouch in the body. 



The male sexual orifice is always situated on the dorsal surface of the 

 cephalotharax and varies slightly in position in the different species. 

 It is usually placed above or slightly in front of the interval between 

 the first and second legs, this being its position in D. folliculoriim. 



