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 &^^ 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 tliis 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 HydracJina 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 



