Species of North Amencan Oligoc/iceta. 401 



constant, number of somites anterior to the budding 

 zone {n of Bourne), it is the normal thing in this species 

 for 71 to vary. The budding zones successively formed 

 in the same worm do not occur at the same place, but 

 a second zone normally occurs one somite nearer the 

 anterior end than the first zone, and the third zone one 

 somite anterior to the second zone, and so on. Of course, 

 a limit is soon reached, anterior to which new zones are 

 not formed. This is usually at XII ] XIII or XIII | XIV. 

 When this limit is attained, the next new zone is formed 

 at some point posterior to the position of the last zone. 

 The following data, taken from the records of a large 

 number of worms which were isolated and reared in con- 

 finement, will serve as an illustration of the usual order 

 of appearance of budding zones. A specimen isolated 

 December 2, 1895, had a chief budding zone at XIV | 

 XV, and a younger one at XIII | XIV. December 5, the 

 beginning of a still younger zone at XII | XIII was 

 visible, while the posterior division of the worm had a 

 budding zone well started at XVI | XVII, and a younger 

 one at XV | XVI. December 7, the posterior division 

 had been freed, and the chief budding zone of the an- 

 terior division was at XIII | XIV. December 11, another 

 worm had been freed, and the only budding zone of the 

 anterior division was at XII | XIII. December 19, an- 

 other worm had been freed, and a new budding zone 

 started at XIII | XIV, in the regenerated portion of the 

 anterior division. Of the six individuals represented in 

 the chain as observed December 5, all but one had be- 

 come free by December 19. Not only is n variable 

 normally, but the position of the first budding zone in 

 the newly formed worms is variable. I have found that 

 in the case of individuals kept in confinement, and so 

 under abnormal conditions, there was a tendency for the 

 first budding zone of new individuals to appear further 

 back than in those living in larger bodies of water. Of 

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