Mrs. Thyiiue and Mr. Gosse on the Increase of Madrepores. 451 



4. Ou one piece of rock was the first gerui of a living Sponge. 

 I watched the shooting forth of its spicula with the greatest 

 interest. It was of very fine texture, and grew to the size of a 

 hazel nut. In the course of the next winter, from want of mo- 

 tion in the water, it had become so covered with dust, that I did 

 not know whether it was alive or dead ; but in the following 

 June, a bright spot appeared on one side, and it threw forth a 

 sporule, whicli attached itself to the rock ; and in a short time 

 a full-grown young Sponge stood beside its parent. 



5. I placed this Sponge in a darkened room, and found the 

 spicula grew most on whichever side was turned to the light. 

 From this time I regularly placed sea-weed in my glass bowls ; 

 but, as I was afraid i might not keep the exact balance required, 

 / sfill had the ivater refreshed by aeration. 



6. I do not know from which, or whether it was from both 

 causes, that my little flock continued to thrive so much ; but I 

 had not many deaths, and they might be from natural causes. 

 A Nereis propagated by gemmation*, and the CaryophyUia; 

 regularly threw out their ova at the usual season. These ova lay 

 quietly upon whatever they were thrown on for one or two days, 

 when they began to rotate, at first slowly, and then more quickly; 

 but I could not secure them, as they were so fine that they 

 passed through or adhered to anything through which I strained 

 the water ; in the mass, to the naked eye, they looked like fine 

 dust. 



7. A week or two after one of these ejectments of ova, I dis- 

 covered with my glass what I at first thought were minute clus- 

 ters of ova, though, on touching them, I found they were really 

 the pearl-like tips of two young Madrepores ; but as the piece 

 of rock on which they were fixed had not been in my possession 

 many weeks, I could not decide whether they were born in the 

 ocean, or were derived from ova which might have adhered. 

 However, as they grew in years, they so exactly resembled one 

 of the older ones, both ni the precise shade of colour and the cen- 

 tral star, that I felt con\dnced that they were truly town-bred. 

 The Madrepores vary so much in their shade of colour, that 

 (excepting the pure white ones) I never procured two full-grown 

 ones exactly alike, both in the centre and the outward part. 



8. In this manner I maintained my marine collection in Lon- 

 don for nearly three years ; and it was examined by very many 

 professed naturalists and other persons interested in natural 



* It was the lower [hinder] ])avt of the animal which came to separate 

 existence. Two red spots, which afterwards became eyes, were the first 

 indications of change. [This mode of increase among the Annelida, which 

 has been denied by a modern naturalist, I have myself repeatedly witnessed 

 in diiFereut species of Nereis, Syllis, and Nais. — P. H. G.] 



29* 



