16 LEPTODORA HYALINA. 



Weismann first met with Leptodora in Lake Constance during the 

 summer of 1873, and supposing it to be new to science devoted much 

 time and trouble to working out its Hfe-history during this and the 

 following year. The principal results to which he was led, as contained 

 in the paper above referred to, are as follows. 



For the capture of Leptodora "Weismann employed a fine net 

 dragged immediately beneath the surface of the water; he notes that 

 wherever they occur they are found in large numbei's. They appear to 

 avoid strong light ; thus, in clear sunshine none are found at the surface, 

 though they may abound at a depth of a few feeL ; at night they occur 

 quite at the surface, but bright moonlight is sufficient to drive them 

 down again. The best time for capturing them is in gloomy weather, 

 towards evening, or on dark nights. Weismann suggests, however, that 

 this shunning of the light may be only apparent after all, and due to the 

 fact that Cyclops, which, according to him, is the chief food of Leptodora, 

 has the same habit, so that Leptodora may be merely following its prey 

 about, instead of being itself directly influenced by hght. Still the fact 

 is one of some interest, and one a knowledge of which may greatly 

 facihtate the capture of this interesting Entomostracon. 



Swimming is effected entirely by means of the posterior antennae, 

 and is comparatively slow. It is only in extremest necessity, when stuck 

 fast, that the abdomen is used for progression, while the feet appear 

 to be never used for this purpose. 



Cladocera may be divided into a littoral gi-oup and a deep-water 

 group, to the latter of which Leptodora belongs. It is only found in 

 water clear from vegetation, and away from the shore. When kept in 

 captivity, algas and particles of dirt soon attach themselves to the 

 s-wimming arms or antennae, and the animals rarely survive so long as a 

 fortnight. They are not uncommonly attacked by a fungus, which grows 

 inwards through the integument and gradually kills them. 



Weismann describes Leptodora as habitually Ijing quietly stretched 

 out in the water, like Corethra, and waiting till its prey comes within 

 reach of its foot-jaws; he considers that the terminal dilatation of the 

 ahmentary canal partially counterbalances the thorax and head, and so 

 aids in the maintenance of the horizontal position. 



The relations of Leptodora to the other Cladocera are discussed by 

 Weismann at considerable length. He points out how the long segmented 

 abdomen of Leptodora is correlated with the rudimentary condition of its 

 carapace, and shows how in such forms as By-thotrephes and Polyphemus 

 we have a gradual increase in the size of the carapace, accompanied by a 

 gradual diminution in the length of the abdomen and fusion of its 

 different segments ; while finally in Daphnia the carapace has grown 

 backwards and downwards, so as to completely enclose the whole animal 



a change accompanied by complete fusion of thorax and abdomen, in 



which no indication of the constituent segments is visible in the adult. 

 The reduction of the body and fusion of the segments is carried to a stil 



