



So-called "Farringdon Sponges" 29 



must be found of proving this than the absence of the radi- 

 ates &c. ; at the same time it must be evident to all, that 

 if we admit the radiates to be an indication of Calcisponge 

 nature, the same argument holds good as to the form of the 



a siliceous one. 



!f 



I do not think that we can place much confidence in the 

 ontogenetic argument ; for although Dr. Charles Barrois, in his 

 Inaugural Thesis (No. 4, p. 27), asserts, upon the authority 

 of Metschnikoff and F. E. Schulze, together with his own 

 observations, that in the development of the sponge-ovule 

 the monactinellid spicules appear first, and views my obser- 

 vations, which are opposed to it, as of no u great importance/ 7 

 because they were made in a single instance (No. 3, pp. 392, 

 393, pi. xx. fig. 16), it is just possible that, if I had con- 

 sidered it necessary to go further, I might, with the material 

 at my command, have found fifty; while, in the figure of the 

 still swimming and unfixed state of the embryo of an Esperia 

 represented in the following plate (fig. 25), I have shown 

 that the whole complement of the spiculation of the species, 

 viz. one skeleton- and three forms of flesh-spicules, may 

 already be seen, as perfect in their forms, although in minia- 

 ture, as in the fully developed sponge — neither one nor the 

 other, so far, appearing first. Thus I do not think the priority 

 of existence of Pharetrospongia among the Calcisponges can 

 claim any support from our present knowledge of the deve- 

 lopment of the sponge-ovule. 



Prof. Zittel lays much stress on the disappearance of 

 " every trace of minute structure " in several of his Calci- 

 spongise when followed by their conversion into silica, as being 

 indicative of an originally calcareous nature (No. 8, vol. iii. 

 p. 368), which seems to accord generally with what I will 

 now mention, viz. : — A short time ago 1 received two frag- 

 ments of flint, each from 2 to 3 inches in their longest dia- 

 meter, one of a black colour coming directly from the " chalk," 

 and the other brown, from the stony detritus of once over- 

 lying " greensand and chalk " in this locality (Budleigh- 

 Salterton, S. Devon), in which the remains of all kinds of 

 sponges are innumerable, although of course much worn. In 

 both fragments there is a fossilized portion of a branched 

 sponge whose digitations were about 5-12ths inch in diameter. 

 This in the black flint appears under the form of a white 

 anastomosing reticulated fibre, that can be seen in the latter 

 through its transparency ; but there happens to be a portion 

 of it outside the flint which never could have been in it, and 

 which must have been directly in the chalk j and this fibre, 



