J. G. WALLER ON THE BURROWING SPONGE. 277 



the year, as it is certain thai something will be learned at opposite 

 seasons, for much remains to be discovered. 



Of the numerous varieties of this sponge in Britain, constituted 

 by Mr. Hancock, Dr. Bowerbank specifies eight, viz., Cliona Gor- 

 gonides, C. Gracilis, C. Howsei, C. Northumbrica, C. Alderi, C. 

 Corallinoides, C. Lobata, C. Vastiflca. All these Dr. Bowerbank 

 disallows, as he says, li they are founded purely on differences in 

 form, without any adequate variations in their structural characters 

 to support such a division." It is so undesirable to multiply 

 varieties, that Dr. Bowerbank's conclusions may be accepted with 

 some satisfaction. 



There is but one form of spiculum properly belonging to this 

 sponge. (Fig. 6.) It is that which the worthy author of the " British 

 Spongiada3 " calls " Enormi Spinulate." Having a preference to 

 Saxon -English, I should substitute "somewhat pin-like," as con- 

 veying a more ready idea to the unlearned, and, I hope, intelligible 

 to the learned. This form pervades all parts alike, whether they are 

 upon the dermal or upon the interstitial membranes. There does 

 not seem much tendency to vary from it to any great degree, and 

 the figures given by Mr. Hancock are doubtless accidental forms, 

 as Dr. Bowerbank suggested, belonging to other sponges, and not 

 to a variety of this genus. 



As the further investigation of this organism is easy, as you 

 have only to select an old and well-drilled shell, I trust my fellow 

 members will soon convince themselves, if I have not done so, that 

 a " boring or burrowing sponge" is about as true a fact in science 

 as the " barnacle goose." 



DESCRIPTION OF PLATE XX. 



Fig. 1 . — Vertical section of oyster shell with sponge. 



a. a. a. dermal membrane ; b. ovaria. 

 Fig. 2. — Dermal membrane, more highly magnified. 

 Fig. 3.— Osculum protruded, dried specimen. 

 Fig. 4.— Ovaria. 



Fig. 5. — Spermatozoa ? and spicules. 

 Fig. 6. — Spiculum. 



