HYDRACHNA. 263 



the period requisite for gaining maturity at about twenty-eight days ; 

 but the young are so minute individually, that, although the spawn had 

 been obviously dissolving, I could not at fii'st discover them ; mere specks 

 to the eye, they could be with difficulty selected for observation. 



Under the microscope such nascent Hydrachna are discovered to 

 have only six limbs, the whole complement is of later acquisition. Their 

 two black eyes, somewhat apart from the front, are sufficiently conspi- 

 cuous.— Plate LXVIII., fig. 7. 



All but one of the young of seven ova from the Hi/drachim ferod', 

 affixed to a glass on the 6 th of September, Plate LXVII. fig. 8, were 

 hatched on the 22d of that month. 



But although gross irregularities embarrass the history of the genus, 

 other observations shewed that the young might be matured in fourteen 

 days. 



On the 23d of July, I committed five large and turgid females of 

 the Hydrachna feroa; to vessels ; spawn appeared next day, of pale-yellow 

 albuminous matter, in three patches, containing three, twelve, twenty- 

 two ova, respectively. Other five, introduced on the 25th of July, pro- 

 duced spots, the first containing thirty ova, the second eighty-seven. 

 Some of the former were hatched on August 8th, thus making the period 

 for reaching maturity extend to fourteen or fifteen days. 



A number of Hydrachnaj having been transferred to a vessel on 

 August 11th, a patch of eight ova appeared next day, and on the day 

 following, other two of eight and twelve ova respectively. 



In the latter, the eyes of the embryos were visible on the 20th, and 

 on the 27th, three had forsaken their prison ; thus attaining maturity 

 in fourteen days. Some remained twenty hours longer, moving and 

 shifting their position within their capsules. 



Additional observations shewed, that, in August, fourteen days were 

 just about enough for the young attaining raaturitv from the date of 

 production by the parent. 



The advance of the embryo is distinctly exposed within the inte- 

 gument as maturit}^ approaches. 



A ruddy tinge distiugushes most of them, and some are stained 



