DEVELOPMENT OF YOUNG TEREBELL/E. 295 



recently, a greater puzzle than the manner in which 

 the Annelidans grow by the acquirement of additional 

 segments could scarcely have been propounded. 



At this period of their growth the little larvae are 

 quite transparent, and although no muscular fibre is 

 as yet distinguishable in their composition, they ex- 

 hibit extraordinary powers of contraction, and keep 

 constantly changing into all sorts of shapes : some- 

 times they shrink into a round ball, sometimes they 

 spread into a round disc with ciliated margins, or 

 constricting themselves into a worm-like form, they 

 attach themselves to the surrounding mucus, from 

 which they have as yet hardly escaped. 



The little Terebellse, having gone through these 

 preparatory changes, now begin to grow rapidly, and 

 their shape becomes more vermiform, by the addition 

 of new segments, which are progressively developed. 

 These rings invariably make their appearance one 

 after another, in the same way as the first-formed 

 segment alluded to above, that is to say, between the 

 tail-segment and that immediately preceding it ; con- 

 sequently, with the exception of the tail, the position 

 of the different rings or segments corresponds exactly 

 with their respective ages, those nearest the head 

 being the oldest, those nearest the tail the most re- 

 cently developed. 



As yet, the young worm has been completely foot- 

 less, but now the lateral locomotive appendages begin 

 to make their appearance in the shape of bunches of 

 hairs, supported on fleshy tubercles appended to the 

 sides of the individual segments, the development of 

 these rudimentary legs being effected in precisely the 



