128 A. OKA. 



almost attained its maxiuuun size. In the nieaiitime, a tliiu sheet 

 of chitin is secreted ])e(\veen tlie two layers of the cystt)geiiOUs cup; 

 it is difficult to say whether it is the product of one or of both layers. 

 This chitinoLis slieet subsequently attains considerable tliickness. 

 We may speak (jf it as the chitinous cup, as it has that shape along 

 with the cystogenous cup. As the latter expands, its mouth narrows 

 and the whole body of the youiig statoblast somewhat flattens, 

 taking the form of a spheroid, the axis of whicli corre^|)onds 

 with tliat (jf the cystogenous cup. The two layers of the cystogenous 

 cup were at first of the same thickness, but now the outer begins to 

 thicken by the increase in heiglit of its cells while the inner undergoes 

 a contrary change. The cells of the latter begin io flatten tirst at 

 the bottom-portion of the cystogenous cup. 



Along the equatorial hue of the spheroidal mass, the outer layer 

 of the cystogenous cup is thrown into a fold, whicli encircles the 

 young statoblast belt-like all around. The belt becomes more and 

 more extensive, and consists, as seen in sections, of two closely 

 opposed strata of cylindrical cells. 



Meanwhile, a second chitinous layer is formed over the chitinous 

 Clip already present. Thus, the chitinous cup c<jmes to consist of two 

 layers ; the outer of which is by flir the thinner. Simultaneously and 

 directly continuous with this outer chitinous layer a thin plate of the 

 same nature is also deposited between the two e[)ithelial strata of the 

 belt. It may conveniently be designated the belt plate. 



The elongated prismatic cells of the outer cystogenous layer, 

 secrete around their basal ends thin chitinous wall continuous with 

 the belt plate or the outer chitinous cup, on which they all sit. I'hey 

 thus bring forth hexagonal caskets open at one end, into which every 

 one of them abuts with their bases. But the wall of these cells does 

 not develope everywhere to the same extent. It keeps very low on 



