66 ON THE RELATION OF Bucephalus TO THE COCKLE. 



B 1. Tube with constrictions. 2. Piece more largely magnified, showing semi- 

 transparency of spheres. 



C. Tube showing contraction of the inner membrane when emptied. 



D 1. Tube. 2. Ovisacs (showing their relative proportions) containing the 

 same eggs, taken from Cockle, April 6tb, 1875. All the ovisacs were filled 

 with eggs. 



Figures E, F, and G are to scale, being rendered about 150 times their 

 natural diameters. 



E 1, 2, 3, 4, 5. Eggs of various sizes taken from ovisacs of Cockles. 



F 1, 2, 3. Epgs taken from both ovisacs and tube in Cockle, April 6, 1875. 



G 1, 2. Eggs taken from ovisacs, April 14, 1875. Tube present, but none 

 found therein. 



Figure H 2 is about 150 times its natural diameter. 



H 1, 2, 3, 4, 5, 6, 7. Spheres and subsequent developments of the embryos 

 taken from a Cockle. 



J 1, 2, 3, 4, 5. Embryos developing ; the dotted line shows the enveloping 

 membrane. 4 and 5. Instances of the extension and retraction, &c, of rudi- 

 mentary filaments. 



K 1, 2, 3. Outlines of the cavities in Bucephalus (? Haimeanus) . 



L. Boot end of filament. 



On the Organic Structure of Flint and of Meerschaum. 

 By M. Hawkins Johnson, F.G.S. 



(Bead May 28, 1875.) 



Given a sufficient amount of earnest investigation, and, I 

 imagine, there is no object in nature that will not prove a mine of 

 delightful surprises. At all events I have found it so with a series 

 of bodies which at first sight appeared most unpromising. I 

 allude to the nodules found in sedimentary strata, and which 

 Geologists have generally dismissed from further consideration by 

 calling them concretionary. 



To two different species of these nodules I wish now to call 

 your attention : — To Flints, which occur in the Chalk, not only in 

 nodules but also in tabular sheets, and to Meerschaum, the sub- 

 stance of which the bowls of tobacco pipes are sometimes made, 

 and which also occurs in nodules and in sheets. 



I have two facts to announce which, I believe, have not been 

 previously noticed. The first is, that the organic structure of 

 Flint may easily be made visible by staining thin splinters with 

 acetate of rosaniline. The second is, that Meerschaum is a fossil 

 sponge. 



