Zoophytes. 207 



taken as an example. After the gemmulc has become fixed and 

 rooted, it becomes elongated superiorly, to the length of an internode, 

 in a bulbous manner. One, and frequently several, of the lower in- 

 ternodes are destitute of cells ; in such cases the pulp undergoes no 

 further change. Superiorly, where the cells are formed in pairs, the 

 elongation of the pulp takes place in the same manner, but is much 

 larger and more bulbous, being of the length and thickness of the 

 two cells. At this time it appears as a diffuse, semi-opaque, granular 

 mass, without any distinction of parts. The first change observed is 

 three darkish spots at the base, at equal distances, in a transverse line, 

 answering to the two cells and the continuation of the stem. At first 

 these spots have no defined edges, but are softened off into the sur- 

 rounding pulp. As they become larger, they become deeper in tint, 

 more defined, and assume the general form of the polype ; the ex- 

 ternal surface of the pulp also becoming more and more translucent 

 as development goes on. At first the sheath is nowhere apparent, but 

 as the edges of the pulp become pale and translucent it becomes 

 drawn from the sheath, and frequently into horizontal folds, as if from 

 a force acting towards the centre. Condensation or organization thus 

 proceeds from below upwards, and from the centre towards the cir- 

 cumference. After the pulp has become separated from the sheath 

 its upper surface becomes serrated, and afterwards organized into the 

 tentacula. The polype thus formed is drawn towards the centre of 

 the cell, which remains closed, so that the polype is entirely included 

 from the water- The upper portion of the cell, which eventually be- 

 comes the mouth, gets more and more attenuated, and finally ruptures; 

 the ruptured edges fall in, and give the cell a funnel-shaped opening. 

 If the bursting of the cell depended on pressure from within, it must 

 be from the polype ; but as the part, before it opens, does not bulge 

 much, so when it ruptures, the edges, instead of being forced out, fall 

 in ; exactly the reverse of what would be expected if the rupture de- 

 pended on internal pressure. In addition to this, it will generally be 

 found that the polype does not touch the upper part of the cell for 

 some time before it ruptures, and hence can have but little or no me- 

 chanical effect in forming the aperture. Though all the cells open 

 in this manner, yet in some the mouth is formed above, and in others 

 by the side ; but the specific differences are prominently formed after 

 all communication between the cell and polype has ceased, and after 

 the cell is ruptured, and hence are probably produced from a power 

 within the sheath itself. In a transverse section of the stem of a 

 horny zoophyte it is found to be annular, the centre of the ring being 



