134 



PENTASTOMIDAE. 



free larva (Fig. 59, n) during later larval life develops into the 

 sub-oesophageal mass and the oesophageal ring, which represent 

 the central nervous system of the adult. The sub-oesophageal mass, 

 in early larval life, is much larger than in the adult animal, and 

 occupies a considerable part of the ventral surface (Leuckart, 

 Figs. 60 and 61, n). 



The rudiments of the genital organs can be recognised early, but, 

 according to Leuckart, it is at first impossible to distinguish the 

 two sexes. A long, unpaired strand lying dorsally to the stomach, 

 the germ-gland (Fig. 60, gel), forks anteriorly to form two strands 

 (the rudiments of the efferent ducts, ag). These two strands 



fna-- 



ma. 



Fig. 62. — Encysted female larva of Pentastomum xiroboscideum (the so-called P. subcylindricum) 

 from the viscera of a mouse, six and a half weeks after infection (after Stiles), a, anus ; 

 ed, proctodaeum ; lit, hook-sac; Ih, larval integument (detached cuticle); m, mouth; ma, 

 stomach ; n, rudiment of the nervous system ; od, oviduct ; oe, genital aperture ; ol, upper 

 lip ; ov, ovary ; rs, receptaculum seminis ; vag, vagina. 



embrace the anterior part of the stomach, and, after reuniting 

 ventrally, open externally in the region of the ganglionic mass (a). 

 There is very little difference in this respect in the male ; the genital 

 aperture in the adult male retains its primitive position in the 

 anterior part of the body, not far behind the mouth. The genital 

 aperture in the adult female is, however, found at the posterior end 

 of the body, quite near the anus (Fig. 62, oe) ; and Leuckart 

 assumes that it has been thus displaced on account of greater growth 

 of the part between it and the mouth taking place simultaneously 

 with arrest of growth in the posterior region. Fig. 61 represents 



