108 



ARACHNIDA. 



only two pairs of limbs, and fully-developed mouth-parts. They differ from the 

 adult chiefly in the absence of the external genitalia. These are developed in 

 the course of two moults, and reproduction can now take place (Nalepa, 

 No. 100). The development of Spluierogyna ventricosa appears still more 

 abbreviated. This Acarid, the female of which is distinguished by the greatly 

 swollen abdomen, is ovo-viviparous. The egg, after being laid, yields the 

 sexually mature male and female, and copulation takes place soon after birth 

 (Laboulbkne and Megnin). 



The course of development may be lengthened by the occurrence of a second 

 nymph-stage following that which proceeds from the larva, and more or less 

 resembling it in form. This is found in Halacarus spinifcr (Lohmann, No. 92), 



-/ie<£ 



Fig 57.— Embryos of Gamasus erassipes after the removal of the external egg-envelope, at 

 various stages (after Winkler), abd, abdomen ; ch, chelicerae ; d, yolk ; eh, the cuticular 

 embryonic integument ; kl, cephalic lobe ; ped, pedipalps ; p l -p i , limbs ; si, caudal lobe. 



and in various Gamasiclae (Reamer, No. 90, "Winkler, No. 106), but it ought 

 to be more definitely ascertained whether these nymphs do not correspond to the 

 pupal stage in other Acarina. It appears, further, that the nymph may be 

 capable of reproduction before it attains the form of the sexually mature animal 

 (Canestrini). This point was established for the Gamasiclae. Berlese 

 distinguishes in this family several ontogenetic series which he describes as 

 normal, and in which the larva, the nymph, and the imago succeed one another 

 in the usual manner, and others which are abnormal, and in which earlier stages, 

 i.e., nymphs, are already capable of reproducing themselves parthcnogcnetically . 

 Such forms do not seem to attain to the complete form of the sexual animal. 



