1 1 Mr. J. S. Bowerbank on Moss Agates. 



spongeous tissue projecting from the inner surface towards 

 the centre of the canal for about one-third of its diameter, and 

 to the sides of these there are oviform gemmules attached in 

 such numbers as to assume in some parts very much the 

 aspect of a cluster of grapes, and against one portion of the 

 side of the canal they are grouped in a similar manner. The 

 mode of their attachment to the plates of tissue cannot be ob- 

 served, in consequence, not only of their position, but also from 

 their crowded state ; but at the terminal edge of one of the 

 plates which reaches nearly to the centre of the canal, there 

 is seen one of the largest oviform gemmules that is w T ithin the 

 field of vision, from beneath which a single fibre of the sponge 

 is seen to emerge and pass towards the centre of the canal, 

 near which it terminates abruptly as if by fracture. There is 

 a gentle curve near the middle of this fibre, in the hollow of 

 which a gemmule is seated that is nearly equal in size to the 

 one adjoining ; so that the position and distinct attachment 

 to the fibre of the sponge of this oviform body removes the 

 possibility of a doubt of their being the true ova or gemmules 

 of the sponge. In the two gemmules last described, the nu- 

 cleus is distinct and well-defined, and is of a size equal to 

 about a third of the smallest diameter of the gemmule ; in 

 some of the others it occupies nearly the whole of their inte- 

 rior, while in the greater number of them it is either very in- 

 distinct or not at all apparent. In all these respects the gem- 

 mules agree perfectly with those before described, as occur- 

 ring in the green jaspers as well as in the other agatized 

 bodies referred to. 



The ova of birds, of fishes, and of reptiles, are always pro- 

 vided by nature with either a bony, horny, or tough membra- 

 nous covering to protect them from the numerous accidents 

 to which they are of necessity exposed until they arrive at 

 maturity. It is therefore but natural to expect that the ova 

 of the sponge tribe should be furnished with a means of pre- 

 servation of a similar description, and thus it is that we find 

 them the last and only remains of the sponge from which 

 they date their origin. The presence of the gemmules in the 

 agates and green jaspers that have been already described, is 

 perhaps the strongest evidence of their organic origin that 

 has been adduced, as in most of the cases cited the organic 

 structure of the fibres has been in such a state of decomposi- 

 tion as to afford by no means the amount of evidence of their 

 animal nature, that they are capable of producing, when ex- 

 amined in a more perfect state than that which has hitherto 

 been described. 



[To be continued.] 



