The largest species of Entomostraca belong to the order Phyllo- 

 poda, and the beauty of their movements through the water and the 

 symmetry of their various organs of motion are truly exquisite. 

 The family Apodid(B contains the largest individuals, though as yet 

 the number of species described is not great. One species of the 

 family was known to Linnaeus, who mentions, in the first edition of 

 his 'Fauna Suecica' (1/46), having seen a specimen in 1728 at the 

 house of a naturalist in London, who told him he had received it 

 from Prussia. Jacob Frisch * had, previously to the publication of 

 the ' Fauna Suecica,' made known and figured a species, specimens of 

 which he had received from Klein, then at Dantzic, who had found it 

 in East Prussia. Specimens of this species were sent soon afterwards 

 by Klein to London to Sir Hans Sloane, and at the very same time 

 ( 1 738) this species was found also in England in a pond on Bexley 

 Heath by the Rev.Lyttleton Brown. Klein's notice, previously sent to 

 Sir Hans Sloane, and Mr. Brown's description, were published simul- 

 taneously in the ' Philosophical Transactions ' of that year. Several 

 species have since then been discovered, natives of various parts of 

 the globe and ha\ang a wide geographical range. They have been 

 found in different parts of Europe, in North Africa, in North Ame- 

 rica, even as high as the borders of the Arctic Ocean, in the West 

 Indies, and in Australia. 



The Family Apodidce (belonging to the Order Phyllopoda) may be 

 thus characterized : — 



Pedes branchiales, paribus sexaginta. Antennce breves, styli- 

 formes, pari singulo. Oculi duo, sessiles. Corpus numerose 

 articulatum, parte majore clypeo magno obtectum. 



The feet, consisting of 60 pairs, are all formed for the purpose of 

 breathing with, and not for locomotion, the first pair alone being pro- 

 vided, in addition to the branchial plates, with organs adapted for 

 assisting the animal in swimming. The first pair are the largest, 

 and after the second pair they become gradually smaller as they de- 

 scend, until the last few pairs become almost obsolete. The animals 

 generally swim on their back, and these branchial feet are in constant 

 motion even when the animal is at rest. The body is cylindrical, 

 elongated, consisting of numerous segments, and the upper half, or 

 more in some species, is covered by a large shield-shaped carapace or 

 buckler. This carapace protects the vital parts, and is furnished with 

 a peculiar structure in its substance for increasing the extent of its 

 branchial apparatus. The antennae are small organs and in number only 

 one pair, short and styliform. The eyes are two in number, compound, 

 lunate-shaped, and are sessile, being placed on the upper and central 

 portion of the carapace. The young have only one eye, which gra- 

 dually disappears as moulting goes on, until the mark merely remains. 

 This is generally described as a third eye, but according to Zaddach 

 the two compound eyes only are provided with optic nerve, pigment 

 and cornea. The caudal segment of the body gives off two long and 

 very numerously articulated cylindrical setae or filaments which are 

 more or less provided with short hairs from each side. 



* Insecten in Deutsclilaud, 1732. 



