136 



The Naturalist. 



tlie temperature ; when cold weather sets in it may be doubled or even 

 trebled. The text-books tell us that the young are liberated by the 

 moulting of the carapace. This is by no means invariably the case. 

 The proportion of such instances, during the observations upon which 

 this paper is based, has been not more than five per cent, of the 

 whole. In several cases the parturition extended over five or six 

 hours, indeed, this might be anticipated, as the development of those 

 nearest the outlet is generally in advance of those lying near the 

 heart. On one occasion the young were forced out when mature by 

 accidental pressure upon the shell, and in another they were liberated 

 artificially by drawing down the body. Both these broods did well, 

 being mature, but to what extent contact with living membrane, in 

 these and higher organisations, is necessary to development is still a 

 moot point. All embryos or ova prematurely expelled invariably die. 



The DapJinifE are extremely prolific, as many as thirty having been 

 counted at a birth, and this number repeated weekly for some months. 

 The young Daphnia cannot be said to undergo a series of 

 metamorphoses comparable to those which the Cyclops passes, but 

 besides the ova already indicated, (which, as in Mysis, may be com- 

 pared to the Marsupials among Mammals,) certain changes are per- 

 ceptible after each of the earlier moultings. At birth, the dorsal 

 spine is long, coarsely serrated and flexible ; and in a day or two the 

 body is too large for the carapace. At the third or fourth day the 

 infant moults its first coat, after which the spine is lance-shaped, 

 finely serrated and directed upwards, being no longer flexible. Eight 

 days later it sheds its second covering, when the spine is reduced to 

 half its previous length. In twelve days it moults for the third time, 

 when, in form, it exactly resembles its parent, the ovaries may be seen 

 to be charged with ova, and the tongue-like process now first appears. 

 Ten days later it moults for the fourth time, and the ova are passed 

 into the marsupium to be hatched ; meanwhile, fresh ova may be seen 

 arising in the ovaries to be transferred to the dorsal cavity within a 

 few hours of its being vacated by its previous occupants. Never more 

 than two eggs are present at the first hatching, the number being 

 increased at each succeeding birth until it reaches thirty, or, if other 

 observers are to be followed, even forty, and any one brood is always 

 all of one sex. After giving birth to its first batch of young, the 

 DapJinia continues to increase in bulk, casting its integument as it 

 grows, and not until after several more moultings and broods does it 

 assume the perfect aspect of the adult. 



