204 Dr. J. E. Gray on the 



spicules which are only modifications or more or less imperfect 

 developments of the same spicule. 



The spicules are divided by Dr. Bowerbank into classes ac- 

 cording to the uses to which he believes them to be applied, 

 and the positions which he says they occupy in the sponge; 

 but as Dr. Bowerbank had no preliminary study of ana- 

 tomy, many of his ideas are most crude and not consistent 

 with physiological knowledge. 



I am not aware of any attempt to divide the spicules into 

 regular types ; but Dr. Oscar Schmidt, in his work on Atlantic 

 Sponges, proposes to divide the Sponges into four great 

 divisions or orders, to which, however, he does not as yet give 

 definite names, thus : — 



I. Spicules of sexradiate type : Hexactinellidce and (extinct) 

 Ven triculitidce. 



II. Spicules anchor-shaped or of pyramidal type : Lithis- 

 tidce, Ancorimdce, Geodinidce, and (extinct) Vermiculatce. 



III. Spicules monaxial, polyaxial, or wanting : HalisarcincBj 

 Gumminece, Ceraospongiai, ChaMiiece, Clialinopsidce, Renie- 

 rince, Suberitidce, Desmaeidince. 



IV. Spicules calcareous : Calcispongice. 



I do not understand what spicules Dr. Schmidt means by 

 mono- and which by polyaxial. 



The siliceous spicules of Sponges are divisible into a few 

 types ; and it has often occurred to me that it would greatly 

 simplify the determination and the description and figuring 

 of the species and genera of sponges if the spicules were ar- 

 ranged in series, showing the forms and modifications in 

 which the different types present themselves to our notice. 

 If this were done after study of the subject and with considera- 

 tion, it would only be necessary in describing a sponge to 

 mention the kind of spicule that occurs in it, instead of figur- 

 ing the same modification of spicule over again every time 

 that it occurrs in any species of sponge. 



I have made such a systematic distribution of the spicules 

 in my own mind. As I am unable, from my bodily infir- 

 mities, to draw them myself or use the microscope, I have 

 tried to induce several persons who do draw spicules and use 

 the microscope to carry out the idea, and have even offered to 

 pay the expense of drawing and lithographing four or five 

 octavo plates, which I believe would be sufficient to show all 

 the chief forms under which spicules occur, and how the spi- 

 cules of each type vary by abortion, position in the dif- 

 ferent parts of the sponge, and by accidental circumstances. 

 I have hitherto failed in having the plan carried out (though 

 more than one person has undertaken to do it), and therefore 



