460 LECTbRE XIX. 



happens to become dried, when the young becomes torpid like the 

 parent, and both revive when they are re-moistened. It is about one- 

 fourth the size of the parent. 



All the Arachnids of the mite family are remarkable for their 

 power of resisting lethal influences, and for the retention of their 

 vitality when torpid and apparently dead. The ova of such are, with 

 still greater difficulty, deprived of their latent life. As all the mites 

 have been endowed with well-developed, if not complex, generative 

 organs, the requisite proof must be satisfactorily afforded of the 

 impossibility of the existence of the eggs of mites in, or of the access 

 of such to, fluids traversed by galvanic currents, before credence can 

 be reasonably given to the statements that acari have been developed 

 by such agency, without any pre-existing eg^, i. e, by way of the 

 " generatio spontanea sen equivocal 



In the genus Trombidium, tlie species are, as in other true mites, 

 represented by distinct males and females ; the testes form one com- 

 pact mass, consisting of a group of red-coloured sperm sacs, attached 

 by a short stem to an annular vas deferens, which opens between the 

 hindmost pair of legs, but receives before its termination the ducts 

 of two vesiculse seminales. In the female the ovarium is large and 

 apparently single, but from it there proceed two oviducts. Mites 

 are oviparous ; the eggs of the Acarus or Sarcoptes Galei, have 

 been detected beneath the epiderm, in itch-patients. The females of 

 the Pi/cnogonidce are known by their filiform jointed ovicapsules, 

 situated in front of the first pair of legs. 



In the true spiders [Araneidre) the males are characterised by their 

 smaller size, their longer limbs, and brighter colours, as compared 

 with the females; but more decisively by the tumid and unarmed 

 termination of the long maxillary palpi ; the parts analogous to 

 '* vesiculse seminales " being lodged here. The essential and the 

 accessory generative organs of this sex are quite distinct and remote 

 from each other : the principle of such separation, which is exem- 

 plified in the relation of the Fallopian tube to the ovarium in Mam- 

 malia, is carried to an extreme in regard to the vesicula seminalis 

 and testis in the spiders. If the analogy of the female parts be here, 

 as in other animals, a guide in the determination of the essential 

 organs of the male, the testes ought to be the two long vermicular 

 tubes, applied to the under wall of the abdomen, which commence 

 posteriorly, either by a simple sac, as in the Mj'gale, or by an oblong 

 vesicle, as in the genus P/ioIcus, the ducts of both of which terminate 

 anteriorly by two approximate orifices, or else by a common opening, 

 as in Tegenaria {fig. 172, k), situated between the two pulmonary 

 stigmata (ib. i, i). These abdominal testicular sacculi are, in fact, laden 



