KEPOllT ON THE PENNATULIDA. P'lB 



In the table given above it will be seen that wlieu this point has been 

 reached growth stops, and in the upper three inches the pitch remains 

 constant at the uuraber 6 ; and the same thing applies to the other 

 specimens as well. Secondly, in five out of the seven specimens the 

 pitch at the upper end is 6, while in the remaining two specimens it is 

 8. If, as we have tried to show above, this number 6 is the limit, 

 tiud is only reached in those parts which have attained their full 

 growth ; i.e., in the parts at or abovit the middle of the entire colony 

 (c/. Fig. 1), then these facts would seem to show that the tops are usually 

 bitten off somewhere about, perhaps slightly above, the middle ; i.e., 

 that in the Oban specimens at any rate, the rachis, if complete, would 

 be something like double its actual length. Concerning the growth of 

 the leaves it is clear that, as iu Fennaiula, the seat of development 

 of the leaves is at the lower end of the rachis. 



Although the leaves get smaller and closer together towards both 

 upper and lower ends of the rachis, yet there is a great difference 

 between the two cases. At the upper end, just as in Fennaiula, though 

 the leaves get smalle:-, the polypes remain fully formed — a point we 

 have been able to coulirm by an examination of the specimens taken 

 by Mr. Darbishire from the haddock's stomach. At the lower end of 

 the rachis on the other hand, not only do the leaves get smaller, but their 

 component polypes get more and more imperfect, and at last (Fig. G, dr) 

 become reduced to mere pit-like depressions of the surface. 



We conclude, therefore, that the topmost leaves are the oldest, the 

 lowermost the youngest : that the seat of development of the leaves is 

 the lower end of the rachis ; and that each actual leaf took its rise at 

 this point, and gradually travelled upwards as new leaves were 

 developed in succession below it ; that the colony grows along its 

 entire length, but that the limit of growth is reached, as already 

 explained, when the distance between successive leaves amounts to 

 J inch ; that this limit is never reached by the oldest or uppermost 

 leaves, which remain permanently small and close together, but that 

 as the colony gets older and older the pitch finally attained by the 

 leaves get larger and larger, until its final limit is reached. 



It follows from this that all the part of a Vir(jularia above the point 

 at which this final pitch is first attain, d has ceased to grow : and the part 

 below it is still growing, but will cease to do so as soon as this limit is 

 reached. 



It will be seen that in many respects this mode of growth agrees 

 closely with that we have described in PcnnatiiJa. In both cases the 

 point of origin of new leaves is the bottom of the rachis, and in both 

 we have the same arrest of development after reaching a certain 

 limit. 



In Virpularia, however, the successive leaves tend to separate from 

 one another to a far greater extent than they do in Pennatula, while 

 in the latter the lateral growth of the individual leaves is very much 

 greater than in Virfjidaria. Another point of difference lies in the 

 fact that while iu Pennatula the several polypes of a leaf ax'e developed 



