LEYDIG OX DAPHNIID2E. 



33 



ambo 2-articulati. Caput breve, infra elongato-productum, antennas 

 anticas obsolescentes versus apicem gerens. 



CEKIODAPHXIA. 



Pedes foliacei numero decem. Corpus fere globosum, capite brevi. 

 Antenna3 anticas niinutae (raro elongatce ?). Testa cellulis hexagonis et 

 pentagonis subtilissime areolata. 



TLEOPIS. 



Caput grande, oculis repletum. Pedes numero octo. Corpus postice, 

 non deflexum, fere rectum ; abdomen crassum extremitate furcatum, 

 setis nullis. Testa postice rotundata. Kami antennarum posticarum 

 3-articulati. 



The whole family I should propose to divide into three sub-families, 

 according to the number of the legs, almost in the manner suggested by 

 Prof. Dana. Firstly, Sidinae, with six pair of foliaceous legs, and con- 

 taining the genera Sida, Holopedium, Latona, and Penilia. Secondl} T , 

 Daphnina), with five pairs of legs, and divided into the three genera, 

 Daphnia, Bosmina, andLynceus. And, thirdly, Polypheiniine, charac- 

 rized by four pairs of legs, and an immense eye. The latter sub- 

 family would comprise Polyphemus, Bythotrephes, Podon, Evadne, and 

 Pleopis. 



Prof. Dana is, however, wrong in describing the head of Polyphe- 

 minae as " oculis repletum," the part thus occupied being, as Prof. Ley- 

 dig correctly points out, only the anterior part of the head. 



On the whole, Prof. Ley(lig's "monograph is worthy of the reputation 

 of its author. The specific descriptions are drawn up with care, and in 

 much detail ; the drawings are clear and good : and though I have not 

 hesitated freely and frankly to indicate the points on which, in my opi- 

 nion, his views are incorrect, or his arguments inconclusive, I am glad 

 to take this opportunity of thanking him for what is undoubtedly a va- 

 luable work on a very interesting subject. There still remain, how- 

 ever, unsolved, many most important questions with reference to the 

 anatomy and development of Daphnia ; and especially an examination 

 into the embryology of the ephippial, as compared with that of the or- 

 dinary eggs, would, doubtless, well reward any one who would under- 

 take it. In a natural condition, indeed, the ephippial egg is so opaque, 

 that its internal condition cannot satisfactorily be ascertained ; but it is 

 probable that this difficulty might be overcome by the use of glycerine, 

 or some other chemical re-agents. The light which is in this manner 

 thrown upon tissues is most surprising; and it is probable that the future 

 progress of histology will depend, at least, as much on the judicious use 

 of chemical agents, as upon that of the microscope itself. 



vol. i. — x. n. R. 



