166 



CCELENTERATA. 



reproductive elements in some Graptolites (if not in all) are matured in 

 special chitinous receptacles, we have an undoubted approach to the 

 Sertularians, with their " ovarian capsules " (fig. 57, c). By Professor 

 Allman, our highest living authority on the Hydrozoa, the Graptolites 

 are regarded as referable to the sub -kingdom of the Hydrozoa, but 

 as presenting us with an ancient and degraded type of this class, in 



which the hydrothecse were occupied 

 simply by mobile amoeboid proto- 

 plasm, instead of by fully-developed 

 polypites constructed upon the Cce- 

 lenterate type. If, namely, we look 

 at the living Plumularians among the 

 Sertularida, we find that the poly- 

 pary, in addition to the ordinary 

 hydrothecse, with their contained 

 polypites, carries a number of cup- 

 shaped processes, which are known 

 as " nematophores " (fig. 58, n). Each 

 of these cup-like appendages is filled 

 with protoplasmic matter, which has 

 the power of emitting amoeboid pro- 

 longations or filaments, strictly com- 

 parable to the " pseudopodia " of the 

 Rhizopods. Upon Dr Allman's view, 

 the " cellules " of the Graptolites 

 were similarly occupied by amoeboid 

 protoplasm, so that these extinct or- 

 ganisms might be compared with 

 Plumularians in which the colony 

 produced nothing but "nemato- 

 phores," and in which the ordinary 

 polypites had not been developed. 

 In the absence of direct evidence, 

 this view can, however, only be re- 

 garded as a more or less probable 

 hypothesis. On the other hand, 

 there are not wanting points of 

 relationship between the Graptolites 



and some of the Polyzoa, and especially those members of the latter 

 class in which (as in Vesicularia and its allies) the cells of the colony 

 communicate by means of a common tube. A further point of affinity 

 between these two groups of organisms is established by the presence in 

 Ehdbdopleura an unquestionable marine Polyzoon of a hollow chit- 

 inous axial tube, which may in many respects be compared with the 

 " solid axis " of the Graptolites. In other points, however, Rhabdopleura 

 is entirely unlike any known Graptolite, and especially so in its general 

 form, and in the fact that it is fixed to solid bodies ; and, upon the whole, 



Fig. 58. Portion of a branch of Anten- 

 nularia antennina, enlarged (after Allman). 

 p, One of the polypites ; n, n, n, Ne- 

 matophores emitting pseudopodial fila- 

 ments of sarcode; n', Nematophore with 

 its sarcodie contents quiescent ; c, Coeno- 

 sarc enclosed within the polypary. 



