8 On the Alteratioyi of Shell- substance hy Hydractinia. 



to signify not only that the law of form is the same both in 

 the vegetable and mineral kingdoms at least (for the glauconite 

 form in this respect is almost typically that of a Conferva), 

 but that vital influence also is t\\Q jyrimum mobile in all — that 

 indomitable power which rules the world independently of 

 man ! 



Having ascertained that the transformed shell, which had 

 been thrown in among the sponges, had been produced by a 

 polype and not by a sponge, I tm-ned my attention to certain 

 branched organisms, or rather their skeletons, which had also 

 been placed among the sponges, and had therefore come be- 

 fore me for examination, when, noticing that they also pos- 

 sessed a clathrate chitinous structure closely allied to that of 

 the polypidom of Hydractinia (fig. 9), while the characteristic 

 feature of most sponges, viz. the branched system of canals 

 terminating externally in large outlets or oscula, was absent 

 from them, I submitted to microscopical examination a por- 

 tion of the stem of a beautiful form from New Zealand, which 

 had been presented to the museum by Sir G. Grey ; and 

 I found not only that it was identical with the structure of 

 the polypidom of Hydractinia, but that attached to its fibre 

 internally, where the water had failed to desti'oy the whole of 

 the soft parts with which the clathrate structure had originally 

 been filled and covered, a few thread-cells still remained. I 

 then sought for the hydrothecte, and found them also. 



Next I took portions from two other species, which came from 

 the Cape of Good Hope — and obtained similar results, so satis- 

 factorily that in many of the thread-cells their contents had 

 become half extruded. 



Finally I examined the two species from Australia which 

 Dr. J. E. Gray, under the family name of ''Ceratellada?," had 

 described and figured provisionally as sponges in the ' Pro- 

 ceedings of the Zoological Society' for November 26th, 1868 

 (p. 575), designated respectively Ceratella fusca and Dehitella 

 atrorubens ; and here, again, I met with similar results. 



Hence it becomes necessary for me briefly to describe all 

 these polyjndoms, beginning with that of the transformed shell, 

 in order that henceforth they may be relegated to their proper 

 place. Were they possessed of their soft parts, and perfect as 

 the Hydractinia of our own shores when carefully dredged up 

 from its natural abode can only be, I should have proposed 

 their being handed over to some one more conversant than 

 myself with this department of zoology : but who can say 

 when perfect specimens of the polypidoms of these species, 

 with all their soft parts recognizable, may be similarly taken, 

 when those we have come from foreign shores, where they 



