II V IK \< UNA. 



the period requisite for gaining maturity at :il>out twenty-eight day* ; 

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

 bwn obviously dissolving, I rould not at first discover them ; mere speck* 

 to the eye, they could be with diluYulty selerted for observation. 



Under the mii-roscope such nascent Ilylnichna are discovered to 

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

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

 cuous. Plate 1.XVI11.. fig. 7. 



All but one of the young of seven ova from the Ili/drachnafcraje, 

 affixed to a glass on the 6th of September, Plate LXV1I. 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 6ve large and turgid females of 

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

 all luminous matter, in three patches, containing three, twelve, twenty- 

 two ova, respeetively. 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 Hydrachna) having been transferred to a vessel on 

 August llth, a pateh 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 maturity from the dat 

 production by the parent. 



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

 gument as maturity approaches. 



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



