ttl. APPENDIX. 



Supplementary Note to Group 11. 



The following Extract is from an Address delivered by Professor 

 Allman, F.R.S., to the Biological section of the British 

 Association, 1873. 



" Let us take an example in which these two principles seem to be 

 illustrated. In rocks of the Silurian age there exist in great profusion 

 the remarkable fossils known as Graptolites. These consist of a series 

 of little cups or cells arranged along the sides of a common tube, and 

 the whole fossU presents so close a resemblance to one of the Sertu- 

 larian hydroids which inhabit the waters of our present seas as to 

 justify the suspicion that the Graptolites constitute an ancient and long 

 since extinct group of the Hydroida. It is not, however, with the 

 proper cells, or hydrothecse, of the Sertularians that the cells of the 

 Graptolite most closely agree, but rather with the little receptacles 

 which in certain Sertularinse belonging to the family of the Plumu- 

 laridse we find associated with the hydrothecse, and which are known 

 as " nematopliores." A comparision of structure, then, shows that the 

 Graptohte may, with considerable probability, be regarded as repre- 

 senting a Plumularia in which the hydrothecaj had never been 

 developed, and in which their place had been taken by the nemato- 

 phores. 



" Now it can be shown that the nematophores of the living Plumu- 

 laridee are filled with masses of protoplasm which have the power of 

 throwing out pseudopodia, or long processes of their substance, and that 

 they thus resemble the Rhizopoda, whose soft parts consist entirely of 

 a similar protoplasm, and which stand among the Protozoa, or lowest 

 group of the animal kingdom. If we suppose the hydrothecse sup- 

 pressed in a Plumularian, we should thus nearly convert it into a 

 colony of Rhizopoda, from which it would difi'er only in the somewhat 

 higher moi-phological differentiation of its ccenosarc, or common living 

 bond by which the individuals of the colony are organically connected. 

 And just such a colony would, under this view, a Graptolite be, waiting 

 only for the development of hydrothecse to raise it into the condition 

 of a Plumularian. 



