Introduction to A?timal Morphology. 371 



at the base of the coxopodite, where there are accessory legs 

 for attaching the ova. There is one family, Pycnogonidae, and 

 seven genera ; some are fish-parasites. 



Order 2. Tardigrada (Z>/^'(2r^/«) — hermaphrodite, minute, 

 worm-like, acardiac, with soft skin ; cephalothorax and ab- 

 domen fused ; four obscure metameres, and four pair of short 

 legs, rudimental, each with three or four curved claws ; the 

 last pair of legs terminal ; mouth suctorial, on a fleshy tube, 

 with two salivary glands, and the antennary jaws forming two 

 piercers, with protrusor and retractor muscles ; oesophagus 

 gizzard-like ; stomach large, with many grape-like c^ca ; 

 ocelli two ; the single ovary and the lateral testes open into 

 the cloaca ; ventral ganglia are further apart than in the last 

 order. They live in damp moss and gutters, and can bear 

 drying with impunity, like Rotifers. They lay a few large 

 eggs during the moulting process, and the slough acts as 

 an tgg sac. There is one family Arctisca. Macrobiotus has 

 no palps or bristles. Echiniscus has marginal bristles. Mil- 

 nesium is palpate, but with no bristles. Emydium has 

 both. 



Sub-class 2. Autarachna {Haeckel) — true Arachnids, with a 

 developed abdomen, rarely undergoing retrogression, usually 

 with respiratory and excretory organs, and ova with partly 

 cleaving yelk. Three orders are included : — 



Order i. Acarina — soft-skinned, with unsegmented abdo- 

 men, united to the cephalothorax ; ocelli none or two, rarely 

 more ; respiration tracheal or dermal ; mouth either mastica- 

 tory, with claw-like antennary jaws, or suctorial, the rostrum 

 or sucking tube being the united pair of mandibular palps, 

 containing the stilet-like antennary jaws ; ventral cord, with 

 one ganglion ; anus ventral ; legs four pair, each with two 

 end-claws ; digestive canal simple, or with caeca, which are 

 often bifurcate at their end, sometimes all directed forwards. 

 There is no heart nor separate liver (except the grape-like 

 cseca in Trombidium, &c.). The tracheae have often few 

 branches or none, no spiral thread, and one pair of stigmata 

 at the bases of the antennary jaws, or of the third or fourth 

 limb-pair. The sexual opening is simple, preanal, often farfor- 

 ward, and the oviduct is often widened into a uterus. The vas 



2 B 2 



