136 ANATOMY AND PHYSIOLOGY 



the operation of the acid by immediately pouring in a 

 quantity of cold water, we shall have preserved their form 

 and have retained the spicula in their natural positions, and 

 have rendered the whole so transparent, as to exhibit their 

 form and arrangement in the walls of the ovarium, either 

 in water or mounted in Canada balsam, in a very beautiful 

 and satisfactory manner. They are packed very closely 

 together, their shafts being in lines radiating from the centre 

 of the ovarium to the circumference ; their distal rotulae 

 supporting the outer surface of its wall, while the proximal 

 rotulse sustain the inner one. Fig. 319, Plate XXII, re- 

 presents a portion of one of these prepared ovaria, and 

 Fig. 319, a, one of the detached spicula. Two views of this 

 form of spiculum are also represented in Figs. 217, 218, 

 Plate IX, and a perfect ovarium prepared by acid by 

 Fig. 318, Plate XXII. 



Carter, in his paper " On the Freshwater Sponges in the 

 Island of Bombay," in describing the birotulate spicula of 

 the ovaria of Spongilla Meyeni and plumosa, species with 

 ovaries of very similar structure to those of S. fluviatilis, 

 states that the spaces between the rotulse are " filled up 

 with a white siliceous amorphous matter which keeps them 

 in position." 1 am indebted to the kindness and liberality 

 of the author for specimens of these species, and I have 

 frequently subjected their ovaries to the action of hot nitric 

 acid, but I have never succeeded in finding any intervening 

 siliceous matter, nor have I ever found any such siliceous 

 cementing material in any other similarly constructed ovary 

 of a Spongilla. 



In the second group of ovaries of the Spongillidae, re- 

 presented by those of /S y . lacustris, in which the walls of the 

 ovaria are supported by elongate forms of spicula disposed 

 at right angles to lines radiating from its centre, the ovaria, 

 in their natural condition, exhibit but very slight traces of 

 the spicula imbedded in their walls. When dried they cup 

 inward like those of 8. lacustris ; but the margin of the 

 cup is thin and sharp compared with that formed in a 

 similar manner by those of S. Jluviatilis, and they expand 

 also in like manner when immersed in water. When 



