60 Anatomy of Sagartia Schilleriana [No. 1, 



In a next stage, subsequent to that above mentioned, cells are 

 observable in which the granular substance is a little reduced, but 

 generally in the right basal corner a dark spot becomes visible with a 

 translucent centre. This is the first distinct embroyonal form (fig. lc). 

 Subsequent to this the upper edges of the sides of the cell and the 

 base become more solid, (fig. Id), then a small spine appears posteriorly, 

 but no aperture as yet in the upper membrane, though it seems to be 

 indicated by an opac-line (fig. 1 e). In the transparent centre of the 

 embryo there are furrows to be observed, radiating from the centre and 

 indicating the formation of the tentacles ; a few thin muscles are also seen 

 attaching the young animal to the posterior end of the cell. After 

 this, the development appears to make more rapid progress ; the body 

 extends, the twisted viscera become perceptible, the membrane covering 

 the aperture is absorbed and the basal string which gives the cell a 

 fixed position developed (fig. 1 jQ. Thus the animal is seen perfect, 

 lying in the cavity of the cell, and the mantle becomes attached all round 

 the margins of the aperture. At a progressive age, the statobasts 

 appear in the posterior portion of the visceral cavity, and the upper 

 membrane of the cell gradually attains a greater solidity by a number of 

 thickened radii or spines. All these stages of cells may often be 

 observed on only a small terminal portion of a large polyzoarium 

 (fig. 1). The basal string is very strong in the young cells, but 

 becomes obsolete in advanced age, as I have previously mentioned, 

 it is therefore only a temporary organ, and not essential to the existence 

 of the animal. 



I also may notice at this opportunity that I observed on one of the 

 polyzoria, small membranaceous tubes attached between each two cells, 

 near their apertural margins. Out of these tubes an organ was 

 voluntarily, and independent of the animals in the cells, projected and 

 retracted. It simply consisted of two fleshy flag dice ; these were 

 probably the so called avicularia the true nature of which, — as appre- 

 hensive organs, — is as yet little known, but the surface was so much 

 covered with different Spongillcd, that I was unahle to trace the 

 immediate condition of these supposed avicularia with the cells 

 themselves. When the polyzoarium was dried, the membranaceous 

 tubes and naturally also their contents disappeared. 



