Anatomy of Daphnia. 255 



The Daphnia longispina of Muller (who quotes Schaeffer, 

 pi. ii. fig. 1.) and many other succeeding authors, amongst 

 others Ramdohr, is merely a variety of D. Pulex, or rather the 

 same insect in a less advanced stage of growth. The D. magna 

 of Straus, pi. xxix. f. 21, 22, is also a mere variety of the 

 Pulex, as I have found them both together in considerable 

 numbers, and running into each other. 



The shell is quite transparent in general, though sometimes 

 reddish coloured. The extremity of the valves terminates in 

 a long spinous tail. Head large, beak sharp-pointed, rami 

 beautifully plumose. The sixth segment of the body has four 

 projections issuing from it, the first being prolonged and 

 curved upwards. The tail of the shell varies much in length, 

 sometimes being short and blunt, which is the D. pennata of 

 Muller, the D. Pulex of Straus ; at others it is long and 

 pointed, and in this state it is the D. longispina of these au- 

 thors. Jurine has, I think, satisfactorily shown these to be 

 mere varieties, the length of the tail varying according to age. 

 In the young it is always long, and becomes shorter as the in- 

 sect advances in age. The male is much smaller than the fe- 

 male, and has the antennas much longer, as already described. 



II. Daphnia vetida (plate ix. fig. 13.). Valvulis non caudatis, ramis plu- 

 mosis, segmente sexto corporis non instructo lobulis. 

 Hab. Ponds and ditches, common. 

 Synonyms. Ungeschwanzter-zackiger Wasserfloh. S chaffer, p. 229. pi. 1. 



fig. 9, 1755. — Daphne vetula. Muller, Zool. Dan. Prod. p. 199. no. 



2399, 1776. — Sulzer, Abgekurzte Geschichte der Insecten, p. 266. pi. 30. 



fig. 10. e, 1776. — Mon. exspinosus. DeGeer, torn. vii. p. 457. pi. 27. 



fig. 9 — 11, 1778. — Daphnia Sima. Muller, Entomostraca, pi. 12. fig. 



11 — 12, 1785. — Mon. Simus. Linncsus, Syst. Nat.3000. no. 25, 1788. 



— Mon. Simus. Manuel, Encyc. Meth. t. vii. p* 723. no. 18, 1792. — 



Mon. laevis. Fabricius, Ent. Syst. t. \\.p. 492, 1793. — Daphnia Sima. 



Latreille, Hist. Nat. gen. et part. t. iv. p. 288, 1802. — Daphnia Sima. 



Bosc. Hist. Nat. Crust., Sj-c. t. ii. p. 283, 1802. — Mon. Conchaceus. 



Donovans Nat. Hist, of Brit. Ins. vol. i. p. 15. pi. 5. fig. 1, 1802. — 



Daphnia Sima. Ramdohr Beijtrcige, fyc, 1805. — D. Sima. Gruithuisen, 



Nova Acta Phys. Med. Acad. Ccesar. Natur. Curios, vol. xiv. part 1st. 



p. 399. pi. 24. fig. 1 — 6, 1815. — Mon. Sima. Jurine, p. 129. pi. 12, 



fig. 1—2, 1820.— Daphnia Vetula. Straus, t. v. pi. 29. fig. 25— 6, 182L 



— Daphnia Sima. Desmarest, p. 373, 1825. 



In this species the valves of the shell are without the spi- 



