34 DEVELOPMENT OF 



dermis, which is at first very soft, but afterwards becomes 

 firmer and horny, and it is in this way that the external 

 horny sheath or tube around these polypes is formed ; and 

 at the same time the spherical extremity of the growing 

 stem from the afflux of the contained fluid is constantly 

 rising, and thus forms a new ring or circle of the sheath, 

 above those already formed. When the stem has attained 

 a certain growth, the motion of the granules contained in 

 the fluid becomes more active and the distension greater, 

 and a so-called cell or cup is formed, which is in fact a 

 polype in a cell. The dilated part is so much expanded 

 as to become, as it were, annular, and it secretes from its 

 inferior surface a horny membrane which forms a parti- 

 tion between the cavity of the stem and that of the cell now 

 in process of formation.* This formation commences by 

 the gradual ascent of the annular portion, which, as it 

 increases in size, secretes a horny membrane from its 

 outer surface, and forms the wall of an inverted conical 

 cell. When this cell has attained its fuU size (fig. 50) all 

 the soft parts recede from its walls, and form a column in 

 the centre ; and it is at this time that the tentacula begin 

 to be formed and the oral orifice to appear (fig. 51.) 

 The animal now pushes against the flat covering or lid of 

 the cell, protrudes its tentacula, and becoming indepen- 

 dent, seizes its food which consists of Cyclops and other 

 smaU Crustacea ; and the nutritious particles, circulating in 

 the interior cavity (or so caUed intestinal tube), become 

 more abundant. This is followed by the shooting out of 

 one branch after another at regular distances from the 

 completely formed polype, which is efiected by the inte- 

 rior soft substance (the intestinal tube) graduaUy accumu- 

 lating at certain parts of the sheath or tube, and causing 

 a rounded projection on it, which projection continues to 

 grow from the stem in the same way that the latter grew 

 from the discoid expansion on the fucus. As soon as the 

 branches have acquired a certain length, a ceU or polype is 



* It is probable that the so-called intestinal canal has never any con- 

 nexion with the cavities of the cells. 



