NATURAL HISTORY OF BHOMPSTON POND. 211 



indigestible residue being cast out at the mouth. Besides, 

 sexually, Hydra reproduces by germination, i.e., a bud grows 

 out at the side of the body (fig. 31, d) and finally becomes a 

 complete and separate individual. Reproduction by fission 

 occurs rarely in the natural state. 



A number of Cercariae (fig. 36), curious little larval forms 

 of the parasitic Distomea, occurred in two of the pond 

 water samples. The specimens had perhaps left an aquatic 

 mollusc (e.g. Planorbis), and were swimming freely before their 

 second host had been found for their encystment. The 

 cercaria larva at this stage possesses a somewhat leech-like 

 body and an extremely motile tail (a). The anterior 

 sucker (b) bears a boring spine (c), which is probably 

 used in effecting an entry into the host ; the alimentary 

 canal and excretory system were more difficult to 

 discern. 



Living parasitically within the lungs of a young frog taken 

 from the pond, the writer found several specimens of a 

 trematode (fig. 37) [probably Amphistomum (Diplodiscus) 

 subclavatus]. The anterior sucker (a) surrounds the mouth, 

 which leads to a dilated portion (c) of the alimentary canal. 

 This bifurcates into two lateral portions (d, d,), each of which 

 seems to end blindly without opening to the exterior. About 

 the centre of the body a posterior sucker (b) is seen. Since 

 one has reason to believe the cercariae (described above) had 

 recently left a Planorbis, and were perhaps swimming about 

 in search of an insect larva in which to encyst, it seems 

 possible, if not probable, that the parasites now under con- 

 sideration and the cercariae are stages in the life circle of the 

 same genus of trematode. 



Nemathelminthes (round worms) are represented by 

 parasitic Nematoda, both in the intestine of the larva of the 

 newt and in the alimentary canal of the frog. Among the 

 aquatic plants, and especially in the mud, there is a plentiful 

 supply of free living Nematoda (fig. 38). 



Nais proboscidea (fig. 39), one of the Chaetopoda, is 

 extremely common, being found among the decomposing 



