OF THE SPONGIAD^E. 145 



and capabilities as the parent mass, we must consider the 

 reproductive bodies so ably and minutely described by 

 Dr. Grant in his paper " Observations on the Structure and 

 Functions of the Sponge/'* not under the designation of 

 ova, but rather under that of gemmules ; and indeed the 

 learned author seems to have entertained some doubt of 

 their being correctly designated by the former term, as in 

 speaking of them in a subsequent portion of his paper in 

 page 14, he says, " since these germs or so-named ova are, 

 &c. ;" I have therefore been induced to arrange them under 

 the designation of Gemmules. 



Dr. Grant describes their first appearance in the sponge 

 in the months of October and November " as opaque yellow 

 spots visible to the naked eye, and without any definite 

 form, size, or distribution, excepting that they are most 

 abundant in the deeper parts of the sponge and are seldom 

 observable at the surface ;" he also states that " they have no 

 cell or capsule, and appear to enlarge by the mere juxta- 

 position of the monad-like bodies around them. As they 

 enlarge in size they become oval-shaped, and at length in 

 their mature state they acquire a regular ovate form." 

 When they have attained a fully-developed condition, they 

 separate from their attachment to the parent and pass out 

 of the faecal orifices. At this period of their existence the 

 learned author states that they are endowed with sponta- 

 neous motion, in consequence of their larger extremity being- 

 furnished abundantly with cilia, which the author describes 

 as " very minute transparent filaments, broadest at their 

 base, and tapering to invisible points at their free extremi- 

 ties." After floating freely about for a period, they attach 

 themselves to some fixed body, adhering firmly to it, and 

 spreading themselves out into " a thin transparent convex 

 circular film." The author further states that " when two 

 ova in the course of their spreading on the surface of a 

 watch-glass come into contact with each other, their clear 

 homogeneous margins unite without the least interruption, 

 they thicken, and produce spicula: in a few days we can 



* 'Edinburgh New Philosophical Journal,' vol. i, p. 16, plate ii, figs. 24-29. 



10 



