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at the extremity of the radiating tubes or their lateral branches. In 

 either case, the formation of the polypiferous cells commences in 

 the same way ; the radical tube, forming the initial trunk of the cel- 

 liferous branch, becomes dilated laterally to about twice its diameter, 

 the dilated portion being separated from the rest by a transverse par- 

 tition, — it being in fact one of the terminal joints or cells of the radi- 

 cal tube, such as 1 have mentioned above, expanded, (fig. 3). 

 The walls of this dilated portion are thinner than the rest of the tube, 

 as if the expansion were eccentric, and its cavity is divided into two 

 by a longitudinal septum. In this way, what may be termed two 

 initial cells are constituted, from which in continuous succession the 

 whole of the rest of the branch appears to be formed. We now come 

 to a more complicated part of the subject. It will be observed 

 in fig. 3 that the whole branch appears to originate in two cells, 

 marked c, c", and farther, that the branch divides dichotomously 

 at tolerably regular intervals, so that the number of secondary 

 branches rapidly multiplies; but if the two primary cells c, c", and 

 those derived from them in continuous succession, were coloured red 

 and blue respectively, it would be found that notwithstanding this 

 multiplicity, the two original colours would be continued uninter- 

 ruptedly to the extremities of two among the numerous branches ; or 

 in other words, it may be said that each primary cell is the origin of 

 a distinct series of polypiferous cells and cups, that each of these 

 series continues single to the last, and that each of them constitutes 

 one half of the cells and cups on the branches upon which it occurs. 

 Tt is clear, then, that at each bifurcation two fresh elements or series 

 of cells are introduced, and it would be found, upon colouring each of 

 these new series continuously throughout, that they also constitute 

 continuous distinct elements of the polypidom, from their origin to 

 the termination of two branches. It is to be borne in mind, 

 however, that any two series or colours are never united in the same 

 internode after the bifurcation of the one in which they first make 

 their appearance. 



It may then be said that the celliferous branch is compounded of 

 numerous distinct series of cells, each forming a continuous chain from 

 its origin to its termination at the ultimate extremity of the branch 

 itself, and that at each bifurcation the due number of fresh series to 

 complete the tale — viz. two — are introduced. 



It remains to point out the mode in which these series of polypi- 

 ferous cells originate, and are afterwards continued. The two 

 primary series, or those marked d and d", arise, apparently imme- 



