138 ANATOMY AND PHYSIOLOGY 



tulate form of spiculimi in the ovaries of Spongilla 

 reticulata is not the only characteristic difference that 

 exists between it and its congener. The form and structure 

 of the ovarium also exhibit marked peculiarities of character, 

 and it is also furnished with a beautiful reticulated spicular 

 envelope or case. In its natural condition the ovary fills 

 the reticulated case, and the coriaceous external surface is 

 pressed into the areas of the network. 



It is usually oviform, but it varies to some extent in 

 its shape. When treated carefully with hot nitric acid, the 

 outer coriaceous substance of the ovarium is dissolved, 

 leaving the inner membrane and the boletiform spicula in 

 situ; their larger terminations being applied to the distal 

 surface of the membrane, while their smaller clavate or 

 stellate ends are projected outward, reaching, in the natural 

 condition, to very near the external surface of the ovarium. 

 The foramen is situated at the small or distal end of the 

 ovary, and differs from that of any other form of the organ 

 with which I am acquainted, inasmuch as it exhibits a 

 tubular elongation outward of the lining membrane equal 

 in length to about its own diameter, causing the ovarium, 

 when prepared with nitric acid, to appear like an oil-flask 

 with a very short neck. Fig. 323, Plate XXIII, represents 

 one of the ovaria prepared with acid, and Fig. 322 one of 

 the cases in which they are contained. 



In Sponyilla Brownii, Bowerbank, there is a still further 

 deviation in the structure of the spicula of the ovary. The 

 shaft entirely disappears, and the spiculum is reduced to 

 the umbonato-scutulate form. They are situated on the 

 outer surface of the inner membrane of the ovarium, with 

 the umbones of the scutellse outwards. This mode of dis- 

 position obviously renders them inefficient for external 

 defence, and the ovaries have therefore been further defended 

 by being inclosed within an elaborately constructed case 

 of reticulated acerate spicula. The ovary is closely em- 

 braced by this envelope, and small elongate masses of its 

 outer surface are projected through some of its interstices, 

 causing it to be more or less tuberculous ; and, from the 

 smallness of the interstices, the tubercles of the envelope of 



