222 



L WFAl IN VER TEDRA TES. 



I'Ki. 212. — To 



worms. It is a marvellous reflection that the w link- nt the su])ertic.ial moulil over any 

 rieli expanse has passed, and will again pass, e\ ery lew years, through the bodies of 

 worms. 'J'he plough is one nf tlic nmst aneient and most valuable of man's inven- 

 tions, but long before he e.xisted the land was 

 in fact regularly |)loughed, and still- continues 

 to be thus plouglied, by earth-worms. It may 

 be doubted whether there are many other ani- 

 mals which have played so important a part in 

 the history of the world as liave these lowly 

 organized creatures." 



The amount of the eastings is strikingly 

 shown by those earth-worms which belong to 

 the genus Perichcvta, for these animals deposit 

 their ejections in remarkable towers, which 

 rise like turrets, with their summits often 

 broader than their bases, to a lieight of two 

 and a half and even three inches. Near Nice, 

 in France, these towers abound in extraordin- 

 ary numbers, and are probably formed by a 

 j^^ — species naturalized from the east. Mr. Scott 

 complains of the trouble they cause in the 

 botanic garden at Bombay : " Some of the 

 near j\ice"°^°^^ "'''""'" finest of our lawns can be kept in anything 

 like order only by being almost daily rolled ; 

 if left undisturbed for a few days they become studded with large 

 castings." The period during which worms near Calcutta display 

 sucli extraordinary activity lasts for only a little over two months, 

 namely, during the cool season after the rains. Hensen believes 

 that the importance of the earth-worm is not so much in tlie pre- 

 paration of liumus as in making ])assages for the roots of plants, 

 and he describes the manner in which the burrows are utilized by 

 pl.ants. Indeed we owe to him the demonstration of the relation 

 of the worms to the fertility of the soil, increasing it as just men- 

 tioned. 



During the mating season the earth-worm leaves his burrow, 

 seeking a mate. The eggs are laid in the ground, and are two or 

 three lines in length. Our figure delineates one of tliem with the 

 enclosed mature embryo, and its top closed by a valve-like struc- 

 ture adapted to facilitate the escape of the worm. The shell 

 g(!nerally contains several yolks, but only one of them usually de- 

 velops. It was once erroneously lielieved that Lumhricus might 

 be nniltiplied' by mechanical section, but although the front part 

 of a divided wonn survives, the back part dies, unless, indeed, 

 when the front includes only the head and a few segments, for 

 then the survival is reversed, the posterior division living on and 

 manufacturing a new head for itself. 



The aquatic Oligochaita (Limicolaj) are very numerous both in species and indi- 

 viduals, and have been separated into four families. 1. PuREORYCTiDJi:, of which the 



