1905 | THE EcGGs OF THE SCARLET WaATER-MITE. 103 
inner side, converting them into effective paddles. At the base of 
the mouth, projecting like a rostrum, are the two simple ocelli, 
black eye-spots, one on each side, provided with a thick translu- 
cent cornea, a thickening of the integument. 
Authorities state that Hydrachna has no heart, but that the 
blood is forced from one part of the body to another by the 
irregular motions of the alimentary canal and the muscles of the 
limbs, as the animal is most restless and in constant movement. 
Breathing is effected by small rudimentary trachee, though certain 
mites breathe by means of the skin. Some of the species allied 
to Hydrachna are parasitic in water-beetles and aquatic Hemip- 
tera, others spend all their lives (young and adult) in fresh- 
water mussels (Unzo0, &c.). Most of them live in ponds and 
streams, but others, like Pontarachna, are marine. The relation- 
ship of these interesting creatures to the true spiders, the 
’ the whale-lice or 
scorpions, the false-spiders or ‘‘ harvest-men,’ 
Pycnogonide, the Chelifers and the Tardigrades or water-bears, 
gives importance to any feature iu their structure or life history. 
If, as some authorities hold, Zzmwlus, the King-crab. be really an 
Arachnid, the Hydrachnide or water-mites, have very ancient 
phylogenetic connections. 
EXPLANATION OF FIGURE ON PAGE 100. 
SCARLET OVA OF THE RED WATER-MITE, Hydrachna. 
1. Three eggs attached by facets to each other amidst Conferve x go. 
a. Scarlet vitellus or yolk-ball. 
6. Thin membrane around the vitellus. 
c. Pitted chorion or egg capsule. 
2. Portion of external capsule more highly magnified. 
3. Group of eggs attached to twig. Natural size. 
