HYDRACHNA. 2G1 



dwelling in harmony during captivity, I was induced to name the crea- 

 ture Hydrachna placida, a character so opposite to that which has been 

 described.— Plate LXVIII., enlarged, fig. 29.* 



Hydrachnte sometimes subsist spontaneously on other animal sub- 

 stances. A'Vlien feeding profusely, they are full, plump, and smooth, of 

 velvet appearance, and remain so after death. Owing to the extreme 

 difficulty of obtaining correct delineations of such active and restless 

 animals, it is probable that most of the figures preserved have been those 

 of specimens after life had fled. All the illustrations presented here, 

 however, were taken from animals during vigorous animation. Never- 

 theless, the characters of many are most equivocal. 



The Hydi'achnos breed at different periods of the year, and, in com- 

 mon with the smaller insects, chiefly during summer. Conspicuous indi- 

 cations of sex were noted long ago by MUller, and more recently also by 

 M. Duges. But there ai'e species wherein the difference is extremely 

 slight, though no resemblance between the male and female exists in 

 others. 



During the union of a species of the Spinifer, the pair remained 

 motionless at the bottom of their vessel. Spawn appears in April, and 

 during the subsequent month, and the maturity of the young has been 

 also postponed as late as the beginning of November. 



Certain species of Hydrachntfi are extremely i)rolific. Some ol" those 

 above enumerated, such as the Hi/dracJina cj'tcndens, affixed more than 

 six hundred ova to the side of a glass jar, where its history could be 

 favourably and distinctly followed. The quantity and fashion of the 

 deposit depends much on the species ; it is generally in patches, and the 

 same spot being resorted to repeatedly by the parent, it occasionally at- 

 tains considerable dimensions. 



The patches consist of twelve, twenty, an hundred and fifty, or a 

 greater number of ova, for the most part sjTnmetrically arranged in a 

 single stratum, on leaves, wood, stone, or whatever else may have been 



* Body, tending to globular, about half a line in diameter. Eyes, two on the anterior 

 surface, black, considerably apart. Limbs with scanty hairs. Colour greyish-brown, 

 lighter on the middle of the back. Taken in a small pond on Braid Hills. 



