142 ANATOMY AND PHYSIOLOGY 



McAndrevni containing ova are represented: (a) contains 

 about the greatest quantity of ova that is found within 

 these organs. In this one the distal terminations of the 

 spicula of the skeleton are still somewhat rounded, and 

 slightly elevated above the common surface ; while in {b), 

 which has been partially exhausted of the ova, the spicula 

 have their distal terminations flat and somewhat angular, 

 and they are level with the general surface, thus indicating 

 a greater age and a fuller development than obtain in the 

 one represented by {a), and not a less amount of secretion 

 of ova, as might possibly be imagined. These circum- 

 stances are strongly indicative of the fact that the ovaria, 

 both in an active and effete state, are permanently seated 

 in the sponge, and that the ova only are discharged from 

 it. So in like manner the existence of the ovarium in 

 SponpUa reticulata and Brownii, Bowerbank, confined 

 within a strong spicula case firmly incorporated with the 

 skeleton, is strong presumptive evidence of their also being 

 permanent organs, and not of the nature of gemmules which 

 separate from the body of the sponge when they arrive at 

 maturity and are ejected through the great faecal orifice. 



Many other species of Geodia with which I am acquainted 

 afford these ovaria in great abundance, aud with some vari- 

 ations in size and form from those in G. McAndrevni, 

 Bowerbank, MS., but in no other sponge are they so large 

 and so completely developed. 



Mg. 325, Plate XXIII, represents an adult ovarium from 

 Geodia McAndrewii with the conical foramen on its summit, 

 and the distal ends of the skeleton spicula flat and angular. 

 Pig. 326 represents a small portion of the surface of the 

 same specimen as seen with a linear power of 308, ex- 

 hibiting the flatness and angularity of their distal apices. 

 Fig. 329, Plate XXIV, represents a portion of a youno- 

 ovarium having the distal ends of the skeleton spicula 

 disunited and acutely conical. Fig. 328, Plate XXIII, 

 represents a portion of a section of an ovarium of G. 

 McAndrewii, exhibiting the radial arrangement of its 

 component spicula. 



In Pachymatisma Johnstonia, Bowerbank, a British 



