Neiv Cladocera of the English Lakes. By Conrad Beck. 781 



the rest of its shell ; the smaller spines are taken out of their old 

 shell which is not completely thrown off and gives the appearance 

 of two pairs of spines. 



The development of this curious spine can be gradually traced 

 through existing species. In Daphnia, the post-ahdomen carries 

 two terminal spines, between which is the anus, and some distance 

 behind these are the abdominal setae. In Daj^Jmella, the terminal 

 spines are similar to those of Daj^hnia, but the abdominal setae are 

 attached to small knobs. In Holopedium, though very similar, 

 they are situated at the end of a long cyhndrical lobe. In Latho- 

 neura, whilst the abdomen still possesses features similar to those 

 of Baphnia, the lobe on which the abdominal setae are situated 

 is much increased in size. In Polypliemus the abdomen has 

 become aborted, whilst this lobe is much lengthened, and in 

 Byihotrephes there is but a small prominence with two spines 

 to represent the abdomen of Baphnia, whilst the long spine 

 takes the place of the lobe on which the abdominal setae are 

 carried. 



The alimentary canal is simple. A labrum covers the entrance 

 of a narrow oesophagus which leads into the stomach; this has 

 no caeca but is considerably dilated at its anterior end. It runs 

 down almost straight to the anus, which is between the terminal 

 spines. The matrix sometimes attains an enormous size, holding 

 as many as from ten to twenty embryos at a time. These are 

 readily distinguished by their large eyes and long spines which are 

 curled round them. The heart is large, triangular, and situated 

 just above the matrix. 



Appendages. — The first pair of antennae (fig. 2) are situated in 

 the front of the head; they are short round processes, and are 

 terminated by three or four fine setae. The second antennae 

 (fig. 3) are jointed to the head below the brain; they are much 

 like those of Bolyphemus ; they each consist of a long basal joint 

 carrying two four-jointed branches, the first joint of each branch 

 is very short and has no set*. The second and third joints of the 

 anterior branch each have one seta, the fourth carries two on its 

 side and three at its apex. In the posterior branch the second 

 joint has one seta, the third two, and the fourth five. AU these 

 are jointed at the middle and finely plumose. 



The mandibles (fig. 4) are long, and are articulated on the 

 shell at the back ; they curve round the body and meet in front of 

 the mouth. In front they have a set of sharp teeth. Although I 

 have dissected several specimens I have altogether failed to find 

 any maxillae. I cannot but think however that there must be 

 some, although they may be rudimentary. 



There are four pairs of legs (figs. 5-8) which projexjt altogether 



