580 GLASS LX. 
Sp. Limnochares holosericea, Acarus aquaticus L. (excl. citatione FRISCHIT et 
Suuzer1), Raseu Ins. 11. Tab. 25, DE GEER Mém. vu. Pl. 9, figs. 15—17, 
Kocn in HERRICH-ScH&FFER Deutschl. Ins. Heft 150, Tab. 24; 2’” or 3” 
long, elongate, very soft, during life vermilion-red : this little animal creeps 
on the bottom of morasses and ditches, and upon water-plants. The young 
animals have six feet, and attach themselves by their sucker to Gerris 
lacustris (p. 443) DuaEs Ann. des Sc. nat., sec. Série, I. p. 161. 
Eylais Latr. Palps with basal joints short, penultimate large, 
last subulate, armed with spines. Rostrum short. Mandibles ter- 
minated by a moveable claw. Ocelli four, approximate in the mid- 
dle of the anterior part of body. Feet long, slender; two posterior 
pilose, the rest ciliated. 
Sp. Eylais extendens, Hydrachna extendens, Muxtu., Hydr. Tab. 9, fig. 4, 
Koon 1. 1. Tab. 21, 22 (according to Kocu Acarus aquaticus L., which 
however is doubtful, and is in opposition to the citation of Rasen from 
LINNZUS). 
Hydrachna MusELu. (in part), Latr., DucEs (and Déplodontus 
ejusd.). Penultimate joint of palps forming with the last a forceps. 
Ocelli two, or four bigeminous, lateral, distant. Feet ciliated. 
Sp. Hydrachna cruenta Murtu., Hydryphantes cruentus Koc, DE GEER 
Mém. vu. Pl. 9, figs. 11, 12, Murturr Hydr. Pl. 9, fig. 1, KocH in 
Herricu-Scu#£FFer D. Ins. Heft 150, Tab. 16. The young animals of 
this and other species with six feet and a sucker, as MUELLER had already 
remarked (pullos ex ovis excludi sex tantum pedibus et proboscide singulari 
instructos), are described as distinct species of Acarida by AUDOUIN, under 
the generic name Achlysia (Mém. de la Soc. d’ Hist. nat. de Paris, 1. 1823, 
pp. 98—109). Dvuaxs has illustrated this subject by continuous observa- 
tions, and has made known the entire life of these water-spiders in its 
different periods, Ann. des Sc. nat. 2e Série, I. pp. 165—171. From the 
eggs, which have been laid in spring in the stems of water-plants perforated 
for the purpose, little hexapod animals come to view, with a large heart- 
shaped sucker, which might be taken for a head, but that the eyes are 
situated behind it, on the anterior margin of the back. After an interval 
they attach themselves to different water-insects (Nepa, Ranatra, Dytiscus), 
and, whilst the abdomen is growing and extending itself into an elongated 
sac, the feet and the sucker remain of the same size. In this form the 
water-spiders were observed by SWAMMERDAM on Nepa (Bybel der Natuur. 
Pl. ut. figs. tv. and v.), and described by him as the eggs of this animal, 
although he had already expressed his doubts whether they were not rather 
distinct animals, which had their increase by sucking the blood of the Vepa 
(blz. 230). In this period the animalcules are named Achlysia by AUDOUIN; 
Duces then calls them nymphs; within the skin the perfect animal is 
formed, like a fly in the pupa coarctata (see above, p. 273). BURMEISTER 
also, simultaneously with Ducks, announced from his observations that 
Achlysia is a youthful form of Hydrachna, OKeEN’s Isis, 1834, 8. 138—142. 
