MICROSCOPIC FAUNA. 173 



4. D. vetula. — Ciliated around the margin of the Carapace. 



5. D. retiadata.—T\\\?, is, as its name imphes, covered \nth 

 fine hexagonal reticulations ; it is destitute of a beak. 



6. D. rotimda. — The spine is very small, and is turned 

 backwards. 



7. D. miicronata. — The head of this species is triangular, and 

 the anterior edge of the shell is straight. 



Five at least of these species may be found in the canal, 

 perhaps all of them ; but as for myself, I have not seen the two 

 last, D. rotunda or vnicronaia^ though the first is common enough 

 about London. I do not propose entering into a minute descrip- 

 tion of this genus, as it must have been often studied by everyone. 

 I will confine myself to some remarks upon portions of the struc- 

 ture that are more difficult to perceive, and thus may have escaped 

 notice. And I will take the Daphtiia pulex^ the best known 

 and most widely distributed, as well as the largest of the seven 

 species. 



Just below the beak are the superior antennae. Figs. 6^, 7/^, 8, 

 which are large and long in the male, but less conspicuous in the 

 female. If you confine the creature so that it shall not be able to 

 move, and turn it with its beak facing you, and manage your light 

 well, you will not only see the antennae clearly, but with a suitable 

 light will make out the arrangement of the setae, which fringe the 

 extremity of each antenna, and you will see that there is a double 

 articulation for each. There is a double spine at the base of the 

 inferior antennae, V shaped. Fig. 6r, the use of which I am unable 

 to determine. These setae are of two kinds, an outer row encir- 

 cling the outer edge of the extremity (these are very short and 

 stout), then an inner group of setse, long and very slender. Holding 

 the Daphnia in the same position, and with a good light the 

 labrum and mouth can be seen, but in order to see the action of 

 the labrum in the act of swallowing, a side view must be had. 

 The particles in the water on which the creature feeds, are carried 

 to the mouth by a current created by the movement of the feet ; 

 they enter between the valves of the carapace at the posterior 

 feet, and pass upwards in a gradually gathering mass between each 

 successive pair of feet, until they reach the mouth, where, I 

 suppose, the superior antennae that I have described, act the part 



