460 DR. J. S. BOWERBANK ON THE SPONGILLID^. [NoV. 24, 



below it. In the dried condition they are semiglobose, much smaller 

 than the envelope in which they are contained, and are strongly 

 tuberculated. When expanded by immersion for a short period in 

 water, they assume a globose form and fill the envelope completely, 

 the large coarse tubercles passing through the interstices of the net- 

 work, and projecting considerably beyond it ; and it is evident that 

 the tuberculation is due to the powerful constriction of the surround- 

 ing network of the envelope, and there are no depressions on the 

 inner surface of the ovary corresponding to the elevations on its ex- 

 terior. 



The manner in which the ovary is encased is very remarkable. 

 There is a single large basal ring of spicula surrounding the foramen, 

 at a distance from it of twelve or fifteen degrees, the whole circum- 

 ference of the ring being composed of seven or eight spicula cemented 

 together by their points, and rarely being more than two spicula 

 thick. From this basal ring other spicula are projected, usually from 

 the apical junctions, and a coarse net or basket-work is thus formed 

 around the ovary — the size and form of the interstices being deter- 

 mined by the length and direction of the spicula. The ovaries are 

 not sessile on the skeleton, bnt are elevated from the fibre on two or 

 three short slender pedicels of spicula, and groups of six or eight of 

 them are often clustered together in the large interspaces of the 

 Sponge, mutually supporting each other by a number of these short 

 pedicels, the greater part of the group having no connexion with 

 the fibres of the skeleton. 



The minute, entirely spined, fusiformi-acerate spicula of the ex- 

 terior of the ovary are disposed without order in the substance of 

 its walls, immediately beneath its surface, and appear to abound 

 more especially in the large tubercles ; and they are not visible 

 under any circumstances until after preparation of the ovary by the 

 aid of a slight boiling in nitric acid. At each end of the spiculum 

 the spines are not very strongly produced, but towards the middle 

 they are frequently as long as its greatest diameter ; they are cylin- 

 drical in form, and terminated very obtusely. The spicula are very 

 minute, and vary considerably in size ; a large one measured 7j-g-j inch 

 in length, and one of the smallest was -g^ inch long. 



The scutulate spicula are imbedded immediately within the inner 

 surface of the ovary. They are closely packed together, and there 

 appear to be two or three layers — the concave surface of the scu- 

 tulum being towards the inner surface of the ovary. The diameter of 

 an average-sized scutulum measured j^ inch. The umbo is conical 

 and acutely terminated. 



Spongilla corallioides, Bowerbank. 



Sponge somewhat fan-shaped, sessile, branching and anastomosing; 

 surface smooth and even. Oscula numerous, small, arranged in 

 linear series on the outer sides of the branches, nearly equidistant, 

 very slightly elevated. Pores inconspicuous. Dermal membrane 

 thin ^ud translucent, aspic ulous. Spicula of the skeleton farcimujo- 



