374 Prof. Allman on the Morphology 



the Hydroida, but would exhibit others at least as strong to 

 the Rhizopoda. Indeed but a step would be needed to convert 

 such an organism into a true rhizopod ; for if the common 

 canal as well as the calicles were occupied by protoplasm, the 

 whole might then be compared to an association of such rhizo- 

 podal forms as Gromia^ united into a composite colony by a 

 common tube filled with a common mass of protoplasm. 



A very general feature in the mode of growth of graptolites 

 is found in the fact that while the entire graptolite continues to 

 increase in length, the denticles which are situated towards the 

 proximal end remain of smaller size than those which succeed 

 them, while, after thus increasing in size towards the middle, 

 they again often diminish towards the distal end, the broadest 

 part of the graptolite being consequently in this case near the 

 middle. It may also be noticed that the denticles towards the 

 base of the graptolite occasionally differ from those which 

 succeed them, not only in size but in form. 



Now, setting aside the undeveloped condition of the hydro- 

 thecee near the growing or distal point of the stem, I know of 

 nothing like this among the living Hydroida ; while, on the 

 other hand, the nematophores of the Hydroida vary in form in 

 one and the same colony, and are sometimes found more or less 

 arrested or otherwise modified towards the proximal end of 

 the branch. 



In support of the hydroid nature of graptolites, the occur- 

 rence of generative capsules in these fossils has been recently 

 adduced ; and as this is a matter of great importance in the 

 present question, we shall here consider the evidence on which 

 it rests. 



Hall has described and figured in one of the double- 

 rowed graptolites {Diplografptus) certain appendages of an 

 irregularly triangular shape, having one angle continued into 

 a narrow band, by which they become attached to the body of 

 the graptolite. They are arranged with considerable re- 

 gularity in two opposite rows, which extend for some length 

 along the sides of the graptolite. These appendages are com- 

 pared by Hall to the gonangia of a calyptoblastic hydroid*. 



I am indebted to Mr. Etheridge for an opportunity of exa- 

 mining a British specimen of a Diiplograptus which carries 

 bodies of undoubtedly the same nature as those of Hall, and to 

 Mr. J. Hopkinson, who had previously examined this specimen 

 and determined its nature, for the inspection of an excellent 

 enlarged drawing of it, which has since formed the subject of 



* Hall, 'Graptolites of the Quebec Group,' p. 32, pi. b. figs. 6-11. 



