OF THE SPONGIADJS. 147 



Ipliiteon panicea. Although the latter sponge is so widely 

 different in structure from the Ilalichondraceous tribes of 

 sponges, its mode of propagation by gemmation seems to 

 be in perfect accordance with them. In Tethea cranium 

 the same mode of reproduction by gemmnles obtains, but 

 the form of the organ is different, and there are other pecu- 

 liarities in its growth and development that are extremely 

 interesting. 



The form of the gemmules is regularly lenticular ; and 

 there are two distinct sorts of them, which are always 

 grouped together. The first is rather the smaller of the 

 two, and has a nucleus of slender curved fusiformi-acerate 

 spicula only. The bases of the spicula cross each other at 

 the centre of the gemmule, and the apices radiate in all 

 directions towards the external surface, but do not, in the 

 fully developed state of the gemmule, project beyond it. 

 The second sort of gemmule is furnished with three distinct 

 forms of spiculum. The first are like those of the genmmlo 

 described above, slender fusiformi-acerate ; the second arc 

 attenuato-porrecto-ternate, the radii being given off from 

 the apex at about an angle of 45 degrees ; and the third 

 form is attenuato-bihamate or uniharnate, and the hooked 

 apices of this form arc projected further than either of the 

 other two forms, but do not pass beyond the 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 indication of either tern ate or hamate spicula, and I am 

 therefore satisfied that they are separate descriptions of 

 gemmule, and that the first form is not a transition state 

 from the young and undeveloped to the fully developed 

 one. 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 charac- 

 terise it. It is highly probable that this marked difference 

 in structure is sexual, and, from the more highly developed 

 condition of the second or large 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 



