REPORT ON THE ACTINIARIA. ■ 5^1 



method of grinding. The integument is composed, as was stated above, of an internal 

 softer zone, and an external zone penetrated by accessory deposits. The latter consist 

 mainly of clear angular fragments of sand ; but there occur also various indeterminable 

 mineral splinters of different colours, and finally, more sparingly, sponge - spicules 

 and Foraminiferal shells.- All these particles lie confusedly mingled, and so closely 

 together as to form a stout external rind ; between them they allow of only thin 

 mesogloea-lamellae, in which are embedded fine nucleated fibres, as well as a few 

 stellate mesogloeal cells. The zone of mesogloea which is soft and free from deposits, 

 consists of a homogeneous matrix, in which sharply circumscribed lenticular cell- 

 islets are embedded in large numbers and of various sizes. They are especially 

 plentiful in the neighbourhood of the endoderm ; but, in passing outwards, every 

 gradation of size, up to fine fusiform structures, is met with. The plane of the 

 long axis of these cell-islets is always circumferential. The nucleated fibres are 

 extremely abundant in the mesogloea ; they extend from the endoderm outwards, 

 their course being sometimes straight, but more generally undulating, with close coils 

 almost like a cork-screw. Besides the contents already mentioned, one ol)serves also 

 the existence of stellate mesogloeal cells, which are sparsely scattered and emit fine 

 processes into the homogeneous matrix. 



" The supporting lamina of the mesentery is Well developed, and presents an antler- 

 like muscle-pennon. At its base passes a canal, filled with cells, and penetrating the 

 mesenteries for their whole length ; in transverse sections through the micromesenteries 

 this appears simple and cylindrical, but forms on the macromesenteries a longer cavity 

 divided up by cross anastomoses. This quite subordinate character accompanies the 

 microtype through all the genera, however difi"erent both externally and anatomically ; 

 no macrotypal form showing even a trace of this mesenterial canal. 



"The sphincter oi Sj^henopus is mesodermal and simple, and is so fiir characteristic 

 that it commences incomparably deeper than in any other knov.-n Zoantliean ; it 

 extends so deeply downwards in the outer part of the body-wall, that, even in the 

 contracted animal, its lowest point lies in the same horizontal plane as the lower end 

 of the stomatodajum. In longitudinal section one can see how, at its deepest point, the 

 bundles of fibrilhc, like small cii'cles, nv ' laid so closely together tluit they appear 

 almost to form a continuous lino. Above they are more extended, and place themse>lves 

 with the long axis perpendicular to the endoderm, from which they are only separated 

 by a narrow lamina of homogeneous mesoghua. In this condition the spliincter forms a 

 system of bacillatc fibrilku-bundles, which arc arranged extremely regularly in the form 

 of a palisade. At the edge of tlie infolding of the body-wall the bundles begin to bay 

 out irregularly, iiml finally sot themselves, on the indrawn part of the body-wall, to form 

 the sphincter proper, a [ilaiv of delicately branching an<l ana.stomosing bundles. This 

 circular muscle increases in bulk downwards, and (onninates below with a rounded 



