10 THE ZOOLOGIST. 



was of opinion that it occurred in the middle of a segment. He 

 never found traces of eggs or other elements. Such, however, 

 have been described by D'Udekem,* Claparede, and others in 

 this species, and in Molosoma and Chcetogaster. The former 

 author, indeed, found these elements mature, yet the example 

 continued to reproduce by buds.t Moreover, in one bud these 

 elements (male) were present. Vejdovsky,! in describing the 

 linear budding of Molosoma, points out that the bud arises 

 irrespective of the presence of a special segment or zone. A 

 slight thickening, the earliest indication of the ganglia, appears 

 in a segment, a pair of short side-nerves following by and by, 

 the alimentary canal and the ventral vessel being continuous 

 with those of the parent. Then a pair of lateral branches arise 

 from the vessel, two ciliated pits form, a pharynx is developed, 

 and the bud is more or less complete. 



In the same group of Worms (Oligochseta), Lumbriculus, 

 though it does not present buds, has a remarkable facility for 

 breaking in pieces in summer and autumn, each piece becoming 

 an independent animal ; while the eggs and other elements 

 appear to be developed only in winter. A tendency to forking 

 in Earthworms has also been described by Dr. Williamson and 

 others. 



On the whole, it is doubtful what advantage buds afford 

 these Oligochaets. If no increase by eggs took place the case 

 would be more simple, but such are found in the parent-stock, as 

 well as in certain buds (Stylaria and Molosoma). In some it 

 would appear to be an accessory mode of increase, since it 

 occurs at a different season from the ordinary method by eggs,§ 

 and perhaps such conditions may be connected with the abund- 

 ance or scarcity of food, or with the drying up of the waters which 

 they frequent. As in the Polychsets, all the forms which show 

 buds are small. 



* ' Bullet. l'Acad. Roy. de Belgique,' 80 an. 2rne ser. xii. p. 243, 1361. 



■\ In the N aides budding is common at all seasons, reproduction occur- 

 ring only at intervals. 



% Op. cit. p. 161, Taf. 1, figs. 16, 29, &c. 



§ Ray Lankester found that the sexual individuals (hermaphrodite) of 

 Chcetogaster on pond-snails ceased to show buds. They were larger than 

 the fissiparous forms, and had an increased number of bristles. 



