REPORT ON CORALS— HYDROCORALLIN^E. 53 



Errina is the only genus of Stylasteridae in which the definite cellular structure of the 

 surface layer of the ectoderm could be determined, although no doubt a similar structure 

 exists in that of all the species of the family. 



In places the cells composing the layer appear to overlap and sometimes to form a 

 double layer, as seen in the figure. Possibly this appearance is due to the action of 

 reagents. 



Nematocysts of two kinds, larger and smaller, occur, and of the usual forms. The 

 larger are mostly gathered into thickly set masses or nematophores (PI. IV. N N), but 

 occur also scattered, or in twos or threes, within the surface layer (PI. XL fig. 10, X). 

 These scattered nematocysts have the appearance of lying within the polygonal cells com- 

 posing the surface layer (PI. XI. fig. 10), as is the case in Hydra viridis, as shown by 

 F. E. Schulze. 1 



The smaller nematocysts occur scattered in the surface layer (PI. XLIV. fig. 10, X), 

 and thickly set in the tentacles of the gastrozooids and outer surfaces of the dactylo- 

 zooids. 



DactyJozooids. — These are simple elongate mouthless conical bodies, closely similar 

 to those of Sporadopora, but somewhat more attenuated in appearance (PI. XXXVII. 

 D Z). They are attached to the bases of sacs which line the cavities of the nariform 

 dactylopores of the ccenosarc, the walls of which sacs are continuous in structure with the 

 surface layer of ectoderm. 



Gastrozooids. — These are cylindrical in form (PI. IV. G Z), with a rounded conical 

 hypostome and four tentacles set in a single whorl at its base. The tentacles are, in the 

 contracted condition, clavate in form. The base of the zooid rests on the style of the 

 containing gastropore, which in the retracted condition of the zooid appears to project 

 into the gastric cavity to a considerable distance as in Sporadopora. The ectodermal 

 covering of the gastrozooids is composed of transparent ovoid cells (PI. XL fig. 4). 

 which form a layer resting upon a substratum containing numerous nuclei and bounded 

 by the basement membrane. The gastric endodermal lining of the zooids is composed of 

 elongate cells of closely similar nature to those occurring in Sporadop>ora. The mouth 

 appears, when closed, as a crucial slit ; four main canals usually lead from the base of the 

 zooid cavity to the coenosarcal meshwork. 



Growth by Budding. — Fresh zooids are added to the colony by means of buds arising 

 from the surface layer of the ccenosarc at points where this is joined by offsets of the 

 superficial canals of the coenosarcal meshwork. Such a bud is represented in Plate 

 IV. D. The part of the superficial layer immediately surrounding the bud is depressed, 

 and forms the sac of the zooid. 



Gonophores. — Only female examples of Errina labiata was obtained for examination. 



1 Uber Jen Bau und die Entwicklung von Cordylophora lacustris, Leipzic, W. Engelman, 1871, Taf. vi. fig. 10. 



