184 



The Naturalist. 



again from the tail to the heart do ally. But at a point on each 

 side, near the base of the arm, where the systemic ascends by the 

 mandible to pass under the stomach, it gives off two currents, a 

 branchial and a tegamentary. The branchial current traverses the 

 five pairs of plumose feet, entering each on the side nearest the heart; 

 (the corpuscles floating freely within the branchial plates,) and, after 

 being aerated, rejoins the systemic current below the abdomen. The 

 tegumentary current passes down the anterior margin of the valves, 

 proceeds along the ventral border, giving off numerous currents on its 

 way that cross the carapace vertically ; the main current continues 

 along the posterior margin of the shell to the dorsal line, along which 

 it receives the vertical currents, and empties itself into the thoracic 

 cavity, immediately above the two inlets to the heart. 



The sensory ganglia of higher animals are represented in the 

 Baplinia pulex by what has thus far been called the brain. It is seen 

 best from below. It consists of two lobes, the posterior, which is 

 the larger, being sub-divided into two hemispheres united by a com- 

 missure, and each hemisphere communicates by another commissure 

 with the anterior lobe, from the front of which the optic nerve pro- 

 ceeds to the eye. The latter is spherical, enclosing within a common 

 membrane twenty apparently round lenses, but said to be pear- 

 shaped when dissected out. In the early embryonic stages two dark 

 specks are present on the head; one develops into an eye, the 

 development of the other is arrested and remains rudimentary through 

 life. It may be seen on the tip of the posterior lobe of the brain, 

 just below the eye. The posterior ganglion gives off nerve fibres to a 

 stellate ganglion situate at the base of the muscular expansion of the 

 labrum. No representative of the ventral chain of ganglia common to 

 other ArtJiropoda has been observed. 



In common with most Crustaceans, the Daphnia pulex sheds its 

 covering at stated intervals. These periodic moultings succeed each 

 other most rapidly during its youth, when the body increasing in 

 size requires a larger habitation. But after its growth is complete 

 the presence of parasitic VorticellcB and Confervcs renders a continuance 

 of the process necessary ; indeed, it not unfrequently happens that 

 the carapace, large antennae, and feet are so infested and overloaded 

 with these incumbrances as to cause them to be incapable of perform- 

 ing the requisite functions for sustaining life, and the victim slowly 

 pines away. The BapTinia pulex does not appear to possess the power 

 of renewing lost- limbs at each moult as most Crustaceans do, No 



