30 Coelenterata. 



the junction of oral disc and column-wall, but at the end of 10 days tentacles 

 had not been formed. 8 larvae, which had shown no indication of trans- 

 formation after having been kept in aquaria for 2 weeks, were put in the dark 

 (loosing most of their zooxanthellse) for 72 hours, and then brought back into 

 full light; 5 of them underwent transformation within 3 days, but they were 

 unable to attach themselves; the other 3 showed only a broadening of the oral 

 disc, and increase in size of the mouth, while still retaining the longitudinal 

 band of cilia in an active condition. The author also made observations on 

 growth of Gorgonids. Specimens of Gorgonia flabellum, which in June, 1910, 

 were 100, 100 and 70 mm. long respectively, in January, 1911, were 135, 

 138 and 100mm., and in July, 150, 150 and 145mm. long respectively. 

 Specimens of Plexaura flexuosa in June, 1910, were 80, 50 and 115 mm. long 

 respectively, in Jan., 1911, were 105, 65 and 150 mm., and in July,, 135, 83 

 and 163 mm. long respectively. Observations on numerous colonies seem to 

 indicate that the norm of size for some species is reached within a com- 

 paratively few seasons. In Gorg. regenerating after removal of a branch, there 

 is formed a complete layer of coenenchyme on the denuded area, which remains 

 free from polyps for some time. The endodermic canals keep pace with the 

 formation of the other tissues, but a considerable time elapses before new 

 polyps make their appearance (as swellings of the canals) at the periphery 

 nearest to the older polyps. The formation of new skeletal tissue, at the end 

 of a cut branch, takes place very slowly at first, but after the new rod of 

 skeletal tissue has attained a diameter equal to that of the older portion, the 

 elongation of the branch is rapid. If the living tissue is removed from the 

 skeleton about the base of a colony, there is no down growth of tissue from 

 the cut surface above the denuded portion of the stem. A violent hurricane 

 in the Tortugas practically destroys the Gorgonids which live in shallow water, 

 the destruction being due chiefly to the tearing of these colonies from their 

 supports, rather than to laceration of the tissues. Such colonies do not live 

 after falling over into a horizontal position; those which had retained their 

 hold suffered laceration of tissues by the waves (in Oct. 1910) and the extent 

 of the injuries could be readily seen in Jan. 1911, but by July, in at least 

 50 % of the specimens, the reparation had been so complete that there was no 

 longer evidence of injury. 



Arndt records Virgularia mirabilis, forma typica and multiflora, from Norway, 

 and suggests these two probably represent only different growth phases of the 

 same form. 



Niedermeyer finds, by means of sections, that in Pteroides griseum the median 

 canals open at the lower end of the stalk by 2 pores. In the walls of the 

 canals which run from the chief canals to the peripheral canal-system in the 

 lower part of the stalk, there are, at certain places, more highly developed 

 circular muscle fibres, which, through not forming definite sphincters, can, on 

 contraction, close the canals. A similar musculature is present in the nutritive 

 canals which penetrate the mesogloea. In the base of the endoderm of the 

 chief canals, there is a circular musculature, which becomes stronger as the 

 lower end of the stalk is approached, and is most highly developed at the 

 lower end of these canals. Evidently, therefore, the various parts of the canal- 

 system can be closed. The muscles of Pennatula are not so highly developed 

 as those of Pt., no doubt in correlation with the more limited water-circulation 

 and dilatation presented by the former. Associated with the muscles of Pt. 

 are neurofibrillse, which issue from ganglion-cells situated below the muscle- 

 layer. 



