962 CRUSTACEA 



this is the Daphnia, pulex, which is sometimes called the ; arborescent 

 water-flea/ from the branching form of its antennae. It is very 

 abundant in many ponds and ditches, coming to the surface in the 

 mornings and evenings and in cloudy weather, but seeking the 

 depths of the water during the heat of the day. It swims by 

 taking short springs ; and feeds on minute particles of vegetable sub- 

 stances, but does not, however, reject animal matter when offered. 

 Some of the peculiar phenomena of its reproduction will be presently 

 described. 



The other group, Phyllopoda, includes those Branchiopoda whose 

 body is divided into a great number of segments, nearly all of which 

 are furnished with leaflike appendages, or * fin-feet.' The two 

 families which this group includes, however, differ considerably in 

 their conformation ; for in that of which the genera Apus and Nebalia l 

 are representatives, the body is inclosed in a shell, either shield- like 

 or bivalve, and the feet are generally very numerous ; whilst in that 

 which contains Branchipus and Artemia, the body is entirely unpro- 

 tected, and the number of pairs of feet does not exceed eleven. The 

 Apus caiwriformis.; which is an animal of comparatively large size, its 

 entire length being about 2^ inches, is an inhabitant of stagnant 

 waters ; but although occasionally very abundant in particular pools, 

 or ditches, it is not to be met with nearly so commonly as the Ento- 

 mostraca already noticed ; in this country, indeed, it is exceedingly 

 rare. It is recognised by its large oval carapace, which covers the 

 head and body like a shield ; by the nearly cylindrical form of its 

 body, which is composed of thirty articulations, and by the large 

 number of its appendages, which amount to about sixty pairs. The 

 number of joints in these is so great that in a single individual they 

 may be safely estimated at not less than two millions. These organs, 

 however, are for the most part small ; and the instruments chiefly 

 used by the animal for locomotion are the first pair of feet, which are 

 very much elongated (bearing such a resemblance to the principal 

 antennae of other Entomostraca as to be commonly ranked in the 

 same light), and are distinguished as rami or oars. With these they 

 can swim freely in any position ; but when the rami are at rest, and 

 the animal floats idly on the water, its fin-feet may be seen in in- 

 cessant motion, causing a sort of whirlpool in the water, and bringing 

 to the mouth the minute animals (chiefly the smaller Entomostraca 

 inhabiting the same localities) that serve for its food. The Branchipus 

 stagnalis has a slender, cylindriform, and very transparent body, of 

 nearly an inch in length, furnished with eleven pairs of fin-feet, but 

 is destitute of any protecting envelope ; its head is furnished with a 

 pair of very curious prehensile organs, which are really modified 

 antennae, whence it has received the name of Cheirocephalus ; but 



1 Professor Glaus has pointed out the relations of Nebalia to the Malacostraca, or 

 higher division of the Crustacea, and has suggested for the group which they re- 

 present the name of Leptostraca. See the Zeitscfir. fur wiss. Zool. 1872, p. 323 ; 

 Claus, Untersuchungen zur Erforschung der genealogischen Grundlage des 

 Crustaceen- Systems, Wien, 1876, as well as ' Ueber den Organismus der Nebaliiden 

 und die systematische Stellung der Leptostraken,' in Arl. Zool. Inst. Wien. viii. 

 (1889), pp. 1-148, 15 pis. ; but a different view is taken by Professor G. O. Sars in his 

 Keport on the Challenger Phyllocarida. 



