THE HYDRACHNA GLOBULA. 
443 
When the mass produced in the body of the Hydrachna by 
the retractation of the legs and palpi is examined after a short 
interval, ten white-looking objects, arranged in two lines or series, 
are to be seen, the hinder ones being the largest. Of these ten, 
eight are destined to be the future legs of the perfect insect, and 
two will be palpi. A white spot indicates the future egg organs, 
and the intestinal canal is observed curved behind and swollen 
near its lower end, where it communicates with a narrow vent. 
It is full of a white substance, which is surrounded by a red 
pulp. After a while the ten white objects elongate, curve, and 
direct their thin free ends forward, and assume the appearance of 
limbs as they grow. The beak is formed at the same time, 
and this and all the structures take on a red tint. The eyes 
of the future perfect spider may be seen under the skin of the 
nymph. The old membranes covering the eyes or corneae are 
still to be seen. All the old skin is furrowed, but it is still strong 
enough to preserve its shape. In due time the new animal splits 
the skin transversely, and comes forth and begins to swim with 
great activity. 
The species of the genus Ncpa and Ranetra of the Hemiptera 
are so frequently covered with these nymphs as parasites, that it 
is very strange that they had escaped careful description before 
M. Duges examined them. Most observers took the pear-shaped 
bodies for eggs, and nearly all the great entomologists considered 
them to be anything but what they really are. The presence 
of six legs in the nymph led Audouin to consider them to belong 
to a special genus of the Arachnida , gifted like the true insects 
with six legs only. 
But it is evident that the Hydrachna passes through a larva 
state and then has six legs, and then becomes a more or less 
physiologically active but probably an immobile nymph — many 
thanks to its host. It then assumes the condition of a free 
swimming spider, whose eight limbs have been developed during 
the end of the nymph stage. These metamorphoses are perfect, 
and the three stages are characterised by different modes of life, 
and by differently looking creatures. But the free swimming 
spider which springs from out of the pupa-like nymph skin is 
not the adult insect, although it has passed through the regular 
