The mesenterial Filaments of tlie Alcyonaria. 15 



say, since the cilia , imlike tliose of the dorsal filaments and of the sto- 

 modaeum, cannot be well preserved and are not visible in seetijns. I 

 think it probable from a study of living animals that the general currents 

 of the gastric fluid are produced by the cilia of the general entoderm, 

 and tend simply to keep. this fluid everywhere uniform. The objeet of 

 the currents produced by the ectodermic bands is probably more special, 

 as pointed out in part III. 



III. Application of these results to special morphological 



Problems. 



We are now in a position to consider the question why the dorsal 

 filaments should show a tendency to carlier and more rapid development 

 in the buds , and we have not far to seek for the answer. The egg- 

 embryology may be takeu to represent more nearly the phylogenetic 

 development, and the presumption is that the late appearance of the 

 dorsal filaments is the more primitive coudition — a conclusion support- 

 ed by other considerations given in part IV. Hence their early devel- 

 opment in the bud is probably due to some special physiological coudi- 

 tion existing in the bud and not in the egg-embryo. A moment's con- 

 sideration shows that this condition is the ne ed for food. All kuowu 

 egg-embryos of Alcyonaria are abundantly supplied with deutoplasm 

 which is sufficient for their needs until the young polyps are able to 

 eat for themselves. The bud-embriyo, on the contrary, has 

 no deutoplasm but is depen'deut upon nutritive fluids 

 brought from the feeding-polyps by the circulatory organs. 

 Hence the early de velo pmentof the ectodermic filaments, 

 and hence also their appearance in the zooids oi Penna- 

 tulida^ which remain permanently in the condition of 

 young buds. The zooids progress in their development simply to 

 the point where their circulatory organs become established. To ad- 

 vance beyond this point would be a sheer waste, since the entodermic 

 or digestive filaments would be of no use to an organism which never 

 takes in food from the exterior. 



We can now understand why the action of the cilia of the ectoder- 

 mic bands should always be upwards. It has been pointed out especi- 

 ally by Koch ^ that the budding of the Alcyonaria is seldom or never 



1 Anatomie der Claviduria jjrolifera, nebst einigen vergleichenden Bemerkun- 

 gen, Morph. Jahrb. Bd. IV, p. 467. 



