488 



ARACIIXLDA. 



H 



be regarded as the anterior appendages, are lost in the course of 

 development. The nervous system is confined 

 to a simple suboesophageal nervous mass, with 

 cesophageal ring and giving off numerous ner- 

 vous trunks. Eyes and organs of respiration 

 and circulation are wanting. The alimentary 

 tract is a simple canal in the middle of the 

 body, which opens by an anus at the posterior 

 end. Special cutaneous glands are present in 

 great numbers and strongly developed. Male 

 and female are distinguished by considerable 

 differences in size and by the different position 

 of the genital openings. While the genita 

 opening of the surprisingly small male lies not 

 far behind the mouth, that of the female is situ- 

 ated near the anus, at the hinder end of the body. 

 The Linguatulida, when sexually adult, in- 

 habit the air chambers of warm-blooded animals 

 and Amphibia. The developmental history of 

 Pentastomum tcenioides, which lives in the nasal 

 cavities and in the frontal sinuses of dogs and 

 wolves, is known from the researches of Leuck- 

 art. The embryos of this species, while still 

 enveloped in the egg-membranes, pass out 

 the nasal mucus on to plants, and thence into 

 the stomach of Rabbits and Hares, more rarely 

 into that of Man. When freed from the egg- 

 membranes, they pierce the walls of the in- 



FIG. 377. Peiitfii<fomuni 

 dcnticiilatum. Young 

 form of P. fren'oide*. 

 O, Mouth; JIf, the 

 four hooks ; D, intes- 

 tine ; A, anus. 



FIG. 378. Young forms of Penfa domum tasnioides (after B. Lcuckart). a, Egg with embryo. 

 b. Embryo with two pairs of hooked feet, JIf and JIf". c, Larva from liver of rabbit. 

 G, Ganglion ; D, intestine ; lid, skin glands, d, Older larva. O, mouth ; A, anus ; Gd, 

 genital g'ands. 



