82 Dr. W. Baird on British Entomostraca, 



cies, without any original matter, are given by Gmelin in his 

 ^ Syst. Natur. Linn.,' 1778 ; Manuel in the ^Encyc. Method./ 

 1792 ; Fabricius in his ' Entotnol. Syst./ 1793 ; Latreille in his 

 ' Hist. gen. et part, des Crust, et Ins.,' 1802 ; and Lamarck in 

 his 'Hist. Nat. des Anim. sans Vert./ 1818 ; but no new species 

 are added. Leach in the ' Supplement to the Encyc. Britann./ 

 art. Crustacea, 1816, and in ' Diet, des Scien. Nat,/ t. xiv. 

 p. 541, 1819, appears to have been sensible that the genus was 

 an ill-formed one, and splits it into two : but with the excep- 

 tion of this, we have nothing new- written upon the genus till 

 Jurine published his " Hist, des Monoc./ &c. in 1820. In this 

 work he has given us a few particulars with regard to the 

 question of their having two eyes, their mode of reproduction, 

 &c. ; he notices several of Miillei-'s species, describes three or 

 four new ones, and hints at the necessity of reforming the ge- 

 nus altogether. These additional species are given along with 

 those of Miiller which Jurine notices, by Desmarest in his 

 * Consid. gen. sur les Crust.,' 1825, but we have no new infor- 

 mation till Milne Edwards published his work on the Crustacea 

 in 1840*. In this work the author shows the necessity for 

 breaking up this heterogeneous genus and reforming it, but 

 does not make the attempt himself, nor do I know of any 

 further attempt having been made till now. 



Habits and Manners. — These insects are found in stagnant 

 w^aters and in slow running streams, amongst the Lemnm and 

 Confervce, &c. which collect in these situations. The males, 

 as far as I know", have not been met Mith or described, though 

 Miiller mentions having seen two, three, and even four in- 

 dividuals fixed to each other and swimming about in that 

 state. Several species are very abundant throughout the 

 spring, autuinn and summer, and may be met wdth in almost 

 every pond and ditch. They are not individually however so 

 prolific as the Daphnia. as they produce only a few^ eggs, ge- 

 nerally two or three only at each laying ; with the exception 

 of the lamellatusf, which has nearly as many as the Daphnia 

 vetuta, and is about the same size. Their mode of reproduc- 

 tion is the same as in the Daphnice, the intervention of the 

 male being not necessary for fecundating the eggs of the fe- 

 male. In one species, the sphcericusX, Jurine obtained by iso- 

 lating the young successively fifteen generations ; and in the 

 striatus^ he followed up the moultings and generations for 

 nine successive periods. " On the 7th of June he isolated a 

 female which had two eggs ; 8th of June, two young ones were 



* The first volume was published in 18.'54; but the third, containing the 

 Entomostraca, was not published till 1840. 



t Eurycercus lamellutus, nob. % diydorus sphcBrkus. 



§ Alona qnadranyu/cnis, nob. 



