HARDWICKE'S SCIENCE-GOSSIP. 



133 



I saw the young escaping from the cocoon. I counted 

 twenty-five of them. They lived over a month, but I 

 had not the proper food for them. From the form of 

 the head and the formidable tusks, &c, I concluded 

 that they were carnivorous, like the voracious larvce of 



Fig. 116.— Nest or cocoon of Hydrophilus. 



the circulation was visible. I made a large sketch of 

 the larva, to enable me tc\ show its form, and omitted 

 the middle sections of the Wy, so that the head and 

 tail only are shown (figs. 117, 118). I have now by me 

 the empty cocoon. The sketch of the beetle and the 

 cocoon are of the natural size, that of the larva is, of 

 course, much magnified : the real length of the larva 

 at a week old was half an inch. 



The following is from Maunder'x "Treasury of 

 Natural History," and would, perhaps, be interesting 

 to your readers : " Hydrophilus, a remarkable genus 

 of aquatic insects, differing from that of Dytiscus 

 only in the structure of the antennse, which, instead 

 of being setaceous, are short, and furnished with a 

 clavated and perfoliated tip or knob. One large 

 species, common in our ponds and ditches, is an inch 

 and a half long, oval, and of a deep brown colour, 

 highly polished. The eggs are laid in a sort of 

 cocoon spun by the female, and coated with a gummy 

 matter which is impervious to water, on which it floats. 

 The larvae are observed to prey on the smaller kinds 

 of water snails, tadpoles, &c, and appear very 

 voracious ; and they remain about two years before 



Fig. 117. — Head of larva of Hydrophilus (mag.) 



Fig. 11S. — Tail oflarva of Hydrophilus (mag.). 



Dytiscus marginatus. The young larvse were very 

 transparent, and the circulation in every part of the 

 body was plainly seen, and formed a beautiful object 

 under the microscope when placed in a very shallow 

 cell ; even up to the end of the curved tail appendages 



they change into pupce or chrysalides. When the larva 

 is arrived at its full growth, it secretes itself in the 

 bank of the water it inhabits, and, having formed a 

 convenient cell, lies dormant for some time, after 

 which it divests itself of its skin, and appears in the 

 form of a chrysalis ; in this state it remains some time 

 longer, when it again releases itself of its exuvire, 

 appears in its complete or beetle form, and as soon as 

 the elytra or wing-cases acquire a sufficient degree of 

 strength and colour, it comes forth from its retreat, 

 and commits itself in its new form to its native 

 element. It is a curious circumstance that some of 

 the species of Hydrophilidse found in this country 

 exceed in size those from tropical climates ; many of 

 the species are, however, very minute." 



