METAZOA ARACHNOZOA. 377 



others ; these are sometimes followed by a pair of palpi 

 (fig. i). Back of these appendages there is a pair of ac- 

 cessory legs in both the male and the female. Singularly 

 enough the work usually done by the female of carrying 

 and thereby protecting the eggs is performed in Pycno- 

 gonids with a single exception by the male (Kingsley). 



There are four pairs of walking-legs 1 which are ex- 

 tremely long and hooked at their ends. Phoxichilidium 

 has, in common with Nymphon, the antennae and acces- 

 sory legs. 



Pycnogonum (No. 935 ; PI. 936, fig. 2), on the other 

 hand, is without antennae in the adult stage, though the 

 larva possesses them. The legs of the male for carrying 

 the eggs are very small (see PI. 936, fig. 2), while they 

 are wanting altogether in the female. This genus has 

 much stouter and shorter walking-legs than Nymphon, 

 and they end in larger claws. 



The Pycnogonids differ from the spiders in having no 

 tracheae nor lung sacs, respiration being carried on by the 

 general surface of the body. 



One of the puzzling forms of animal life is Linguatula 

 (PI. 937 ; No. 938). It has been placed among the 

 Worms, the Crustacea, and at present is considered as a 

 near ally of the mites and, therefore, placed among the 

 Arachnida. Its parasitic habit has completely disguised 

 the adult, and were it not for the larva one would be 

 wholly unable to classify it. This larva (PL 937, fig. i, 

 lower side; fig. 2, upper side of L. proboscidea Rud.) is 

 an internal parasite. Its body shows no separation into 

 cephalothorax and abdomen. The jaws are horny ; the 

 two pairs of jointed legs are similar in shape and are pro- 

 vided with hooks. The larva finds its way to the liver or 

 the lungs of its host a reptile, the python, in this 

 case and becomes encysted (fig. 3 ; fig. 4, taken from 

 the cyst; fig. 5, the same enlarged). 



1 In regard to the different views held concerning the third and 

 seventh pairs of appendages, see Morgan, loc. '/., p. 31. 



