X] LUMBRICUS 157 



surrounds its body in the neighbourhood of the thirty-second to the 

 thirty-seventh segment. As the band passes over the openings of 

 the oviducts in the fourteenth segment it carries away with it a 

 certain number of ova, and as it passes the orifices of the sperrna- 

 thecae between the eleventh and tenth and tenth and ninth 

 segments, some of the spermatozoa which have been received from 

 another individual are squeezed out. Besides ova and spermatozoa 

 the cocoon contains a certain amount of a milky and nutritive fluid 

 in which these cells float ; this is probably supplied by certain other 

 glands in the skin of the earthworm. At the moment the last 

 segment, that is, number one, is withdrawn, the anterior end of the 

 cocoon contracts and closes, and as the posterior end of the band- 

 like ring passes over the head it also closes, so that the cocoon lies 

 in the earth as a closed vesicle containing eggs, spermatozoa and a 

 nutritive fluid. The spermatozoa fuse with the ova and from the 

 fertilised ova, by division into a number of cells and by the 

 differentiation of the cells into muscle cells, epithelial cells, 

 digestive cells, nerve cells, etc., a young earthworm is built up. 

 Before being hatched out of the cocoons the young embryos are 

 nourished by the milky nutritive fluid in which they float. 



In Great Britain there are several species of earthworm, which 

 are grouped into two genera, viz. Allolobophora, with 

 fourteen species, which, with one exception, have the 

 prostomium not dove-tailed into the peristomium ; 

 and Lumbricus, with five species, in which the prostomium is com- 

 pletely dove-tailed into the peristomium. The above account has 

 been taken from the anatomy of L. herculeus, the largest of our 

 indigenous species, but with the exception of a few minor details 

 the account applies to most British earthworms. 



Order I. Oligochaeta. 



The sub-order to which earthworms belong, the Terricolae, 

 are for the most part inhabitants of the land, and occur widely 

 distributed over the earth, being, as a rule, only absent from sandy 

 and desert soils. Some of them are aquatic but not many. On 

 the other hand the allied sub-order the Limicolae are for the 

 most part denizens of fresh water. A few Limicolae possess gills 

 or finger-like processes well supplied with blood-vessels which take 

 up oxygen from the surrounding water. Both sub-orders contain 

 numerous genera and families ; together they form the order 

 Oligochaeta, which is characterised by being hermaphrodite, by 



