PORIKERA. II. II 



bundles of spicules spread in a more or less fan-like or penicillate way; the fibres are generally of a 

 length of 3— 4 mm . The dermal membrane is supported by the projecting bundles of spicules, and is 

 provided with no skeleton of its own. The fibres and bundles of spicules that support it, are, however, 

 often far from being perpendicular on the surface, and accordingly, when a piece of the skin is viewed 

 under the microscope, it may appear, as if there was a reticulation in the skin, the fibres under it 

 being also seen. In the fibres of the skeleton some spougin is seen, which, although not abundant, 

 coats the fibres completely. As mentioned above the fibres are thickest at the base of the sponge, 

 and the spongin is also most distinct here. Below the fibres pass into a thin basal membrane formed 

 by spongin, and provided with scattered spicules; it is directly fastened to the substratum, from which 

 it is easily separated, and then it shows a smooth surface. 



Spicula; a. Mcgasclcra are styli or very slightly marked subtylostyli; most frequently they are 

 straight, sometimes quite slightly curved. They are thickest in the middle, and thus a little fusiform, 

 the greatest thickness being not rarely nearest to the pointed end. The point is evenly tapering, but 

 not long. Most frequently they are slightly restricted a little below the rounded end, and thus ap- 

 proaching to subtylostyli, but the restriction is not rarely imperceptible or wanting. The length is 

 between o-6— o75 mm , most frequently approaching the latter size; sometimes it may go down to o-5' n[ ". 

 The thickness is between ca. croi— o-02 m,n . Finer spicules, developmental forms, occur, but in very 

 small number. The specimen described by Topsent I.e. has somewhat larger megasclera; they are 

 stated to be 0-935— o-o,8o mm . b. Microsclera : Of these are found isochelae palmatse of three different forms, 

 and sigmata. 1. The largest chelae are of a peculiar shape, Carter calls them weaver's shuttle- 

 like »; they are narrow, the side-edges of the two alae are parallel, and the alae continue far down 

 along the shaft, so that only a short space is left in the middle where the cylindric form of the shaft 

 is seen. The shaft is straight. The side-edges of the tooth are likewise about parallel, or slightly 

 converging towards the end, and the end of the tooth is rounded. When the tooth is seen from the 

 front, it appears to have a thickened edge, but this is owing to the fact that the sides are curved 

 inwards. When the chela is viewed from the side, it is seen that as well the sides of the tooth as 

 the alae on the shaft are curved inward so as to meet each other at the ends of the chela. Seen from 

 the side the tooth most frequently bends a little outward at the end, while the outermost point is 

 again bent inward in a claw-like way; the latter bend, however, is in so far only apparent, as it is 

 owing to the bending in of the edge. The edge of the tooth being thus bent inward all round the 

 tooth becomes hollow on the inward side. The tooth is generally of about the same length as the 

 alae, and its position is about parallel to the shaft. At its basal end the axis is seen as a little oval 

 tubercle. These chelae are sometimes somewhat twisted. The length is rather varying, from 0-08— 

 o-i2" ,m , and the greatest breadth, a little above the middle of the tooth, is ca. o-oi3' nm . Of these chelae 

 developmental forms are found; the youngest stage observed was formed as a fine staff having at 

 both ends a large part recurved with a round curve, and the recurved ends were finely tapering 

 (PI. VIII, fig. id). This staff thus represented the axis of the chela, alae and tooth having not yet been 

 formed; the development now consists only in the growing forth of the alae and the tooth. The develop- 

 mental forms have the full length of the chela, the youngest stage was thus measured to o-i ram . 

 2. The middle form of chelae is somewhat smaller and broader; also in these the shaft is straight 



