104 INVERTEBRATE ANIMiLS. 



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 diiFer only in the somewhat 

 higher morphological differentiation of its coeuosarc, 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 hydrothecre to raise it into the condition 

 of a Plumularian. 



" Bringing, now, the Evolution hypothesis to bear upon the question, 

 it would follow that the Graptolite may be viewed as an a,ncestral form 

 of the Sertularian hydroids, a form having the most intunate relations 

 with the Rhizopoda, that hydranths and hydrothecse became developed 

 in its descendants, and that the Rhizopodal Graptolite became thus 

 converted in the lapse of ages into the hydroidal Sertularian. 



" This hypothesis would be strengthened if we found it agreeing with 

 the phenomena of individual development. Now such Plumularidae as 

 have been followed in their development from the egg to the adult 

 state do actually present well- developed nematophores before they 

 show a trace of hydrothecee, thus passmg in the course of their embryo- 

 logical development through the condition of a Graptolite, and recapi- 

 tulating within a few days stages which it took incalculable ages to 

 bring about in the palseontological development of the tribe." 



NOTE. 



Six tiers of drawers occupy each side of the block supporting the 

 table-case, and not four tiers as indicated by the frontispiece. 



i). Marples, Printer, Liverpool. 



