16 Coelenterata. 



in the interior of the embryo and a little later the cells at the periphery 

 form a definite ectodermic layer ; these cells are ciliated and without yolk glo- 

 bules. Just beneath the ectoderm there is a layer of undifferentiated embryo- 

 nal tissue laden with yolk surrounding the irregular central cavity. 



Torrey describes the results of experiments on regeneration in Renilla, 

 and finds that colonies may readily regenerate lost parts. They exhibit a 

 strong polarity; when a peduncle is removed by a transverse cut an axial 

 polyp is never regenerated in its place, and vice versa. There is an anterior 

 limit beyond which anterior pieces do not regenerate posteriorly, and a posterior 

 limit beyond which posterior pieces do not regenerate anteriorly; these cor- 

 respond to the limits of the budding zone. The colonies regulate themselves 

 in a plastic fashion when cut in certain ways, e. g. obliquely. It is thus pos- 

 sible to obtain two new colonies, one of which retains the original peduncle 

 with a lateral polyp displaced into the position formerly occupied by the axial 

 polyp. If the oblique cut make with the colonial axis an angle greater than 

 45 there is no displacement of the lateral polyp, the extirpated axial polyp 

 regenerating as though it alone had been removed by a transverse cut. When 

 a lateral group of polyps is removed by a longitudinal cut it regenerates a 

 new peduncle approximately at a right angle to the cut surface and nearly in 

 the axis of the chief lateral polyp of the group. 



Studerl 1 ) describes the Alcyonaria obtained by the "Hirondelle" near the 

 Azores, near Newfoundland and in the Bay of Biscay. The greater part of 

 the work consists of diagnoses of the numerous new species most of which 

 have been briefly described by the author in 1890-1. The following genera 

 are represented Clavularia, 2 (1 n.), Erythropodiwm 1 n., Schizophytum n. 1, 

 Alcyonium 2 n., Sellonella 1 n., Anthomastus 1 n., Paraspongodes 2 (1 n.), Eu~ 

 nephthya 1 n., Gyropliyllum n. 1, Pennatiila phosphorea 2 var., Virgularia 1, 

 Acamlla 2, Chelidonisis n. 1, Stachyodes 2, Plumarella 1 n., Caligorgia 1, Acan- 

 thogorgia 6 (3 n.), Muriceides 1 n., Acamptogorgia 1, Clematissa 1 n., Bebryce 1, 

 Eimicella 1 n., Stenogorgia 1, Seirpearia 2 (1 n.), Verrucella 1 n. For fission in 

 Schizophytum see Bericht f. 1891 Coel. p 23. 



Weissermel argues against the attempt to derive Alcyonaria from tabulate 

 corals, pointing out the numerous difficulties met with and especially the con- 

 stantly recurring differences in the minute structure of the skeleton. The 

 skeleton of Heliolites is not built up of a series of radial calcareous fibres 

 fixed to an axis as in Heliopora, and in no tabulate coral hitherto described 

 is the formation of the skeleton from separate spicules authenticated, as it is 

 in the Alcyonaria. But while the form of the tabulate corals has remained 

 quite unchanged since Palaeozoic times, their minute structure cannot have 

 been totally altered. Moreover in ontogeny, the calcareous skeleton of Alcyo- 

 naria is composed of separate spicules which may however fuse later. This 

 points to the fact that the Alcyonaria are descended from ancestors which 

 possessed a soft skin and not from such corals as the Tabulata which have 

 compact tubular skeletons. 



(C. Hydrocorallia.) 



