GRAPTOLITOIDEA. 



213 



lished that the "virgula" is invariably developed in all types of the 

 Graptolites, and the name of Rhabdophora, proposed for the group 

 by Professor Allman, is, therefore, not wholly appropriate. 



"With regard to the reproductive process in the Graptolites there are 

 strong grounds for supposing that the generative elements were 

 developed in specially modified polypites, or " gonophores," after 

 a manner analogous to that which occurs in the Hydroid Zoophytes 

 generally. In some cases, these generative buds may have been 

 destitute of a hard covering, and therefore incapable of preservation ; 



Y~V h 



VI 



Fig. 94. — a, Monograptus colonics, enlarged ; b, A fragment of Monograptus priodon; c, Mon- 

 ograptus colonus; D, Monograptus Clingani; E, Monograptus spinigerus ; F, Monograptus 

 attcnuatus; g, Monograptus Hisingeri, all greatly enlarged, s, Sicula ; v, Virgula; c, Coen- 

 osarc; h, Hydrotheca ; in, Aperture of hydrotheca ; sp, Apertural spine. (After Lapworth.) 



but in other cases there is evidence of the existence of chitinous 

 receptacles, of larger size than the hydrothecae, and of different form, 

 which may be compared with the " gonangia " or " ovarian capsules " 

 of the recent Sertularians, and may be supposed to have lodged the 

 reproductive zooids. Thus, occasional specimens of certain of the 

 diprionidian Graptolites have been found to carry on their sides 

 singular horny sac-like structures, which can hardly be regarded as 

 anything else than as of the nature of " gonangia." Moreover, it is 



