BEITISH SPONGIAD^. 87 



inner surface of the tough dermal envelope of the gemmule 

 when in the adult state. 



I have examined a great number of these gemmules, 

 and could never find in the form first described any indica- 

 tion of either ternate or hamate spicula in any of them, 

 and I am, therefore, satisfied that they are separate de- 

 scriptions of gemmule, and that the first form is not a 

 transition state from the young and undeveloped to the 

 fully developed form ; and in like manner I have closely 

 observed the second form, and have always found it uniform 

 in character, and furnished with the whole three forms of 

 spicula that characterise it. 



It is highly probable that this marked difference in 

 structure is sexual, and from the more highly developed 

 condition of the second or largest form that it is the female 

 or prolific gemmule, but on this point we must at present 

 be satisfied with conjecture only, as, although I have 

 searched 'diligently for spermatozoa, in both forms of 

 gemmule, and in the surrounding sarcode, I have not 

 been able to detect any thing resembling them. 



This occurrence of two distinct forms of gemmule in the 

 same sponge is the first case of this singular fact that has 

 come under my observation, and is the only indication of pro- 

 bable sexuality in the Spongiados that I have ever met with. 



The short porrecto-ternate spicula of the gemmule ai-e 

 jLth inch in length, and the unihamate ones ^th inch in length. 



When a gemmule is viewed in water by transmitted 

 hght, and a power of 150 linear, we find that it is thickly 

 but indistinctly maculated. 



2, Tethea Collingsii, Bowerhank. 



Sponge. Massive, sessile, depressed. Surface uneven 

 and rugged. Oscula and pores inconspicuous. Dermis 

 thick and dense ; dermal membrane pellucid, furnished 

 abundantly with minute acerate tension spicula ; and, 

 also, with attenuato-stellate retentive spicula, large 

 and small, and also cylindro-stellate spicula, ininute. 



