POLYZOA INFUJfDIBULATA. 261 



natural limits set to the magnitude and duration of the poly- 

 pidom, except what arise from accident or extrinsic causes. 

 The original polype and its immediate successors may grow 

 old, languish, and die ; but the solid cells remain in their 

 connection as a root and fixture, while the newer races, which 

 have sprung up towards the outskirts, continue their work, 

 generation following generation in rapid and ever -multiplying 

 successions. The polypidom in this respect resembles a tree 

 in its growth : the trunk and main branches have stood years 

 and centuries, but the increase has been made by annual 

 shoots and renewals, and the last know only vigour and power 

 of renewal. And as the form of the tree depends on the 

 fashion of its ramifications, so that of the polypidom on the 

 mode of evolution of its cells, for every part of the axis is 

 not equally organised to produce buds, nor the same parts 

 in all. Hence if the primitive cell has only one point fitted 

 for this gemmation, the polypidom will be builded up in 

 a catenated chain ; if the cell has two points, two series 

 of cells are formed ; and so on with more. In several 

 species the multiplication goes on in a regular arithmetical 

 progression, but in others the cells are heaped together 

 without apparent regularity, as in the Alcyonidise, where 

 the softness of all the parts seems to allow of a non-regu- 

 lated succession of buds. The general disposition of the 

 cells, however, in this order, is certainly after the quincunx, 

 affording examples which the learned Sir Thomas Browne 

 would have gladly adduced in proof that " Nature geome- 

 trizeth and observeth order in all things, and of the generality 

 of this mystic figure." Nor indeed were they entirely over- 

 looked by this observant physician : " The spongy leaves of 

 some sea-wracks," he says, " Fucus, Oaks, in their several 

 kinds, found about the shoar, with ejectments of the Sea, are 

 over-wrought with net-work elegantly containing this order 

 (the quincunx) : which plainly declareth the naturality of this 

 texture ; and how the Needle of Nature delighteth to work, 

 even in low and doubtful vegetations."* 



So many of the Polyzoa have been ascertained to be her- 

 maphroditical, that it is fair to conclude they all are so.f 



* The Garden of Cyrus, p. 33. Lend. 1686. folio, 

 t Van Beneden sur le genre Laguncule, p. 1 6. 



