264 HYDEACHNA. 



scarlet or vermilion, derived perhaps from the contents of the .abdomen. 

 Hence, where the parent is unknown, it is difficult to determine the par- 

 ticular species occupying the spawn. 



The decaying leaf of an Iris bore a patch of several hundred ova on 

 the 15th of September. Its colour brightened in proportion as the em- 

 bryos approached maturity. Plate LXVIII. fig. 14. Some had escaped 

 on October 26th and 27th, but many remained on the 2d November, 

 when one of beautiful vermilion quitted its capsule during microscopical 

 observation. This young animal must consequently have remained there 

 at least forty-eight days. Plate LXVIII. fig. 15. Thus the period be- 

 tween production and maturity is infinitely varied and most irregular, 

 whether from being dependent on the species, as is probable, regulated 

 by the temperature of the atmosphere, or influenced by both. 



If the spawn be in a watch glass, the young rush out of the water 

 on escaping from the capsule, and run very actively on the bare glass 

 itself. 



M. Dug6s remarks, that such nascent Hydrachnos run on the 

 surface of the water, and on the sides of the vessel, believing also, that 

 before attaining perfection, they may, as parasites, infest such insects as 

 frequent the water.* 



Hydrachnse descend amidst their element on the approach of cold ; 

 and they seem to seek shelter among mud, or the roots of plants, through- 

 out winter, or until aroused by the reviving influence of Spring. 



In certain years they abound, in others they are rare, and some 

 seasons seem to favour the multiplication of particular species ; possibly 

 atmospheric influence has as much effect on the spawn as on the parents 

 themselves. 



In May 1802, hundreds in great variety could be taken in a recent 

 artificial pond, whereof the superficies did not exceed a quarter of an 



* Much information will be derived from the perusal of two memoirs on the genus 

 Acarus, by the acute naturalist here referred to. He there partitions the genus Hydrachna 

 of the Linnoean system into several subdivisions, chiefly derived from external characters, 

 and explains the metamorphosis of the young in their progress to perfection. Annulet de 

 Sciencei Naturellet, Sec. Ser., torn. I. Paris 1834, in 8vo. 



