34 



somewhat rugose film containing minute granulations, the whole be- 

 ing of a darker colour than the mass of the fibre, as represented in fig. 

 1 , PI. iii. which exhibits a portion of the fibre of Spongia officinalis 

 deprived of its mucilaginous or fleshy coat, and fig. 2, which repre- 

 sents a fibre upon which it has been retained; and also in fig. 14, 

 which is from a fibre of the West Indian species. 



It is probable that these granules are the incipient gemmules of the 

 sponge, for in some instances I have found pellucid circular bodies, 

 containing a central nucleus, embedded in a fine membrane that coat- 

 ed the fibre. There is much difficulty in finding these bodies in situ, 

 in consequence of their great transparency, but when the membrane 

 happens to have been disturbed and partially removed they become 

 very apparent, and present the appearance represented in fig. 3, PI. iii. 

 when viewed with a power of 1000 linear. When these nucleated 

 bodies were observed upon the fibre, the granulated appearance seen 

 in fig. 2, PI. iii. was not apparent, and as the nucleated bodies are 

 considerably larger than the granulations, there is a great degree of 

 probability that they are the gemmules of the sponge in an advanced 

 stage of their development. 



I am not aware that any author has described the gemmules of the 

 keratose sponges, but those of numerous species of Halichondria have 

 been so minutely examined and described by Dr. Grant in the 'Edin- 

 burgh New Philosophical Journal,' and they agree in their general 

 character with the bodies under consideration, so closely, as to leave 

 but little doubt in my own mind that they are really the gemmules of 

 the sponge in one of their earliest stages of development ; but this is 

 a question which cannot be satisfactorily determined without an exa- 

 mination of the living sponges under the most favorable circumstances. 



The greater part of the fibres consists of cylindrical transparent 

 threads, frequently anastomosing, and varying very considerably in 

 their size. This portion of the tissue is destitute of spicula ; but there 

 often occur, dispersed amid this form of tissue, large flattened fibres 

 running in a straight direction, and not anastomosing so frequently 

 as the surrounding cylindrical threads ; and it is in this portion of 

 the tissue that the spicula are found, embedded in its centre, as repre- 

 sented in fig. 1 a, PL iii. 



Sometimes there is only a single spiculum embedded in the centre 

 of the fibre, while at others two, and occasionally three or more, are 

 grouped together, and here and there one will project a third or half 

 its length from the side of the fibre. 



The spicula vary very considerably in their size and proportions, 



