HARDWICKE'S SCIENCE-GOSSIP. 



245 



spine. Eye spherical, bluish black ; composed of 

 about twenty crystalline lenses. It is quite included 

 within the shell, but it is very distinct, and its quick 

 and rotatory (to some extent) motions are observable 

 with ease. Labrum with a large hairy swelling at 

 the end. Jaws composed . of a strong process, 

 furnished at the extremity with four horny spines ; 

 three of them are incurved. Mandibles, a fleshy- 

 looking body ; geniculated, and furnished at the end 

 with three small teeth. Legs ; there are five pairs. 

 Female, first pair, three-jointed ; on outer edge of 

 second segment are three minute processes, with four 

 (often five) long, jointed seta?. Last segment small, 

 with a few setse. Hale : they are more slender here, 



between it and the back of the animal until hatched, 

 when the young make their escape. Frequently, 

 however, the little things still stay on in their safe 

 retreat, until more able to fend for themselves. The 

 eggs are large and, as a rule, few in number, but 

 surrounded by such advantages that there are few 

 but what reach maturity. This is evidenced by the 

 fact, that they are seen in such battalions, as to 

 actually colour the water, as before mentioned. 

 Baird remarks, that they will sometimes assemble so 

 as to form a belt, a foot or more in breadth and ten 

 or twelve yards in length, and that the whole belt 

 will pass round the pool. Let a shadow fall across 

 this enormous assembl}', however, and it disappears 



Fig. 147. — ij Daphnia. pulex : a, inferior antennas ; e, superior antennae ; c, heart ; D, ova ; 2, Daphnia Sch&fferi; 3, first pair of 

 legs ; 4, second pair of legs ; 5, third pair of legs ; 6, fourth pair of legs ; 7, fifth pair of legs ; 8, mandibles ; g, labrum. 



and there is a claw at end of second joint. Seta 

 arising from terminal joint long, and floats from 

 underneath carapace. The second, third, and fourth 

 pairs are branchial. Joints with segmented, plumose 

 setae and a plumose setae branchial plate. The fifth 

 pair are slightly different to the foregoing. The 

 portion analogous to the branchial plate is rounded 

 and afilamentous. 



Life-history. — The interesting feature connected 

 with Daphnia, is the fact that it does not undergo 

 metamorphosis. At their birth the young Daphnise 

 are as much like their parents externally as they 

 may possibly be, except in size, but after successive 

 moults this is remedied. The ova, on its escape from 

 the ovary, does not leave the shell, but remains 



directly, only to reappear at the removal of the 

 disliked object. 



As in Cyclops, so in Daphnia, one fecundation 

 suffices for many successive generations (some com- 

 pute it at six, but I believe more) ; the number of 

 eggs laid varies nearly each time of deposition, for as 

 they advance In life, their number increases from the 

 first deposition of one to, later in life, sixty in some 

 species. It is general that one batch of eggs is 

 restricted to one sex : thus, in a male batch it would 

 be extremely rare to find females, or in a female batch 

 to find males. All moulting and oviposition ceases 

 as the cold weather draws on, and many are of 

 opinion that the frost destroys the creature, leaving 

 the egg unharmed, they hatching out on the return 



