The prostalia lateralia ■whicli protrude radially from the sides of the sponge 

 are most numerous just beloTv the bulging equatorial zone. Scattered prostalia 

 lateralia however occur right dovm to the lo'wer end of the sponge. Most of 

 them are stout, situated singly, and protrude several centimeters ; some are smaller 

 and arranged in protruding bundles. The lateralia are very hable to be broken 

 off : one only finds them intact in the very best specimens. 



The prostaUa marginalia do not increase in thickness uniformly with the 

 growth of the sponge. In young specimens of walnut-size they are much thicker 

 than in specimens full grown. In the former we generally find 6-10 marginalia, 

 600-800 a thick, situated in a row on each marginal prominence. In the latter 

 there are about a hundred marginalia only 200 h- thick, or under, on each promi- 

 nence. Specimens under walnut-size, again, have more slender marginalia than 

 those of walnut-size. In such small specimens their thickness decreases with 

 the size of the sponge, until in specimens 15 mm. high the marginalia are 

 again, as in the fuUgrown sponge, only 200 /^ thick. This curious abnormity 

 formerly induced me to establish a distinct species, Pheronema circumpalatum, 

 for the walnut-sized specimens with stout marginalia. It seems that two gener- 

 ations of marginalia succeed each other, the spicules of the first, growing imtil 

 the sponge has the size of a walnut, attain a thickness of 600-800 /* and are 

 then thrown off ; the more numerous slender spicules attaining a thickness of 

 only 200 /*, composing the second generation, are then produced and replace those 

 of the first. Possibly there may also be two generations of lateraha and basalia, 

 for I sometimes found spicules iu the small root-tufts of waLaut-sized specimens 

 considerably stouter than any in the much longer root-tufts of full-grown 

 specimens. 



The root-tuft increases in size as the sponge grows. In small specimens, 

 •5 mm. in diameter, it consists of about 40 spicules protruding 2 cm., which are 

 not arranged in bundles. Such root-tufts are surrounded by spicules transit- 

 ional between the basalia and the lateralia, in such manner that there is no 

 distinct limit between them : the former pass gradually into the latter. In spe- 

 cimens 10 mm. in diameter the root-tuft is composed of 5-6 bundles, each contain- 

 ing 4-6 closely-packed spicules. The bundles are about 1 mm. apart and form 

 a tuft clearly distinguished from the lateralia surrounding it. As the sponge 

 grows these bundles and the spicules composing them increase in number and 

 in size ; f ullgrown hand-high specimens possess 20—30 bundles, each of a finger's 

 length and composed of about 50 spicules. The centres of the large hypodermal 

 pentactines which support the dermal membrane protrude slightly, forming, as 

 in other Pheronema-species, low prominences. These spicules are not disposed 

 so regularly as in the other species, their tangential rays not being disposed 

 exactly parallel or vertical to each other. The superficial skeleton-net which they 

 form consequently appears unusually ii-regular. These hypodermalia measure 



