The male sexual organs consist of a pair of testicles lying in the body 

 between the insertion of the fourth pair of extremities ; from these proceed vasa 

 deferentia, which tarry the spermatozoa to a vesicula seminalis, situated betwee i 

 the testicles ; beneath this lies the genital plain, bounded in front, as a rale, by a 

 strong curved band of chitin and beru'ing a penis, which miy be long or short, 

 and either soft or chitinous. As accessory reproductive organs may be mentioned 

 the copulatory suckers on the ventral surface of the abdomen, and in some genera 

 the enlarged third extremities, which are then used as claspers. 



The female sexual organs consist of a post-anal opening leading by a tube 

 into a receptaculum seminis which opens into the anterior end of the oviduct. 

 The ovaries are two irregular masses lying near the posterior end of the body, 

 and opening at their anterior end immnliately in^o the wide oviduct, w Inch is very 

 often seen to contain a relatively large egg. The oviduct open-? between or in 

 front of the insertion of the third pair of extremities by a longitudinal slit which 

 is protected by a thin chitinous plate on each side, and in front by a dark brown 

 chitinous bow called the shemit or lyra. 



The surface of the body is covered with a thin chitinou-5 cuticle which on the 

 belly and sides and across the middle of the cephalo-thorax is marked with fine 

 folds like thcse seen on the palm of the hand. The back in adult specimens, in 

 some species, with the exception of the part above mentioned, is covered by two 

 slightly darker, finely granular plates, one over the anterior portion and jaws. 

 the other over the abdomen and hinder part of the cephalo-thorax. The epiuitra, 

 as the dark brown bands of chitin are called which run in from the insertion of 

 the feet and support them, constitute the whole skeleton. Chitinous hairs and 

 bristles are scattered regularly over the body, being disposed as anterior and pos- 

 terior dor-als, laterals, and anals, together with others on the body and extremities. 

 As they appear to be of definite number, siz'j, and position, in the dilt'erent forms 

 th-y are of great importance in defining the species. The extremities are in two 

 pairs on each side, the anterior being situated on tlie anterior end of the body, and 

 alike in males and females. The third and fourth pair, on the contrary, are 

 situated rather far back, and usually different in the two sexes. In some of the 

 genera the third pair of extremities is greatly enlarged, forming large claspers, and 

 they are then no longer used for locomotion but only in copulation. 



The difl"erent stages of growth areas follows : First the egg, about twice as 

 long as thick, and rounded at each end. Second, the hexapod larva, and, as 

 shown by M.M. Kobin and ileguin,* it is, curiously enough, the third and not the 

 fourth pair of legs which has not yet appeared. Third, after the larval state these 

 little animals acquire the possession of eight legs, but otherwise are much the 

 same as before, no sexual organs up to this time being developed. This condition 

 has been called the nymph stage. Fourth, after the next moult the males 

 assume their mature form ; the females have to pass through another stage 

 before they come to sexual maturity. la this stagrf they ar^ a little larger than 

 the nymphs, but otherwise difi'cr very slightly from them. Fifth, In females the 

 complete sexual development, an egg being usually seen to be present in the 

 oviduct. It i-i only in the mature stages that the plate on the dorsal surface of 

 the abdomen is present in those species which possess it; in the earlier stages it 

 is always absent. 



Habitat. — They live among the feathers of mo.st of our birds, being found on 

 the wings in living and recently killed specimens, but on birds that have become 

 stiiT and cold generally close to the bo iy, where th'>y may sometimes be fouad 

 for four or five days after deafli. 



ANALGES, Nitzsch, 1819. 



General form of the body very different in the two sexe.=, the third pair of 

 extremities being greatly enlarged and terminated by ttrong claws. The fourtli 



* Journal dc V Aiiat et dc ht Phyxiol, 1S77, p. 233. 



