Mr. J. S. Bowerbank on the Structure of Sponges. 131 



chondria, the curved, double-pointed, needle-formed spicu- 

 lum, fig. 5. Plate III. The variation in their diameters is ex- 

 ceedingly great, one of the smallest measuring but the seven 

 thousand one hundred and sixtieth of an inch, while the frag- 

 ment of a large one imbedded near it (fig. 6. Plate III.) was 

 the seven hundredth of an inch in diameter. There are nume- 

 rous grains of sand and other extraneous matters imbedded 

 in the fleshy substance along with the spicula. 



Upon examining with a power of five hundred linear the 

 outer surface of the small portions of the sponge which I 

 had removed from the specimen, I observed patches of a 

 very fine reticulated structure, which is beautifully and faith- 

 fully represented by the artist Mr. Aldous, at fig. 7. PI* HI* 

 It is composed of a very minute fibre, imbedded in a trans- 

 parent membrane. The interstices are somewhat irregular 

 hexagons in the piece represented in the figure ; but in an- 

 other part of the same small piece of sponge, which did not 

 exceed the eighth of an inch in length, some of them w ere 

 nearly square, while others were elongated to such an extent 

 as to assume the form of nearly regular oblong areas. The fibre 

 of this cuticular network has every appearance of being solid ; 

 it is extremely minute, not exceeding the ten thousandth 

 part of an inch in diameter. The average diameter of the in^ 

 terstices of the reticulations figured is the two thousandth of 

 an inch, while the fibre of the mass of the sponge varies 

 from the three hundredth to the three thousandth of an inch 

 in diameter; and the smallest spiculum I could find was, as 

 before stated, the seven thousand one hundred and sixtieth of 

 an inch at its greatest diameter. From the whole of these cir- 

 cumstances, there is little doubt that this delicate reticulated 

 membrane is the true cuticle of the sponge. Upon examining 

 a small slice from near the base of the body of the sponge, I 

 had the satisfaction of observing the groupof gemmules,or eggs 

 of the sponge, represented by fig. 8. PI. III. ; but I could not, 

 from the cutting in my possession, satisfactorily determine 

 whether they were attached to the fleshy substance of the 

 sponge, or to the fibrous skeleton ; although in several of 

 them, which had apparently been disturbed by the removal of 

 the thin slice from the sponge, the point of attachment of the 

 gemmule was very apparent when viewed with a power of five 

 hundred linear. The diameters of the gemmules varied consi- 

 derably ; the largest I could find measured the three hundred 

 and fifty- fifth part of an inch, and the smallest the one thou- 

 sand one hundred and forty-third of an inch in diameter. 



Upon examining another species of keratose sponge in a 

 similar state of preservation, which is in the collection at the 



K2 



