700 
PROFESSOR WILLIAMSON ON THE STRUCTURE AND 
these various topics, since it would not only be valuable in a physiological point 
of view, but also in its practical application to geology. We already obtain faint 
glimpses of the prevalence of some general law, through the operation of which a 
number of varied products appear to be developed out of one primitive blastema. 
Chondriform and membraniform bone, kosmine, dentine, ganoin, enamel, cartilage, 
fibro-cartilage and fibrous periosteum, appear to be mysteriously linked together, 
and to possess some community of nature which is not yet fully revealed. The pre- 
sent attempt to add to the existing stock of facts, has only shown to me how wide 
a field still remains unexplored, which field must be worked out before we can fully 
comprehend the laws regulating the osteo-genesis of fishes. 
In conclusion, I have again to acknowledge the kind assistance which I have re- 
ceived from Sir Philip de Malpas Grey Egerton, who has facilitated my investiga- 
tions in many ways, especially in supplying me with specimens for examination, 
which I could not otherwise have obtained. 
Description of the Plates. 
PLATE XXVIII. 
Fig. 1. Scale of a Ctenoid fish from the Bay of Dulse (Mexico). Nat. size. 
Fig. 2. Vertical section of the same scale, made in the direction of the dotted line, 
fig. lab. Magnified 5 diameters. 
Fig. 3. Still more highly magnified view of a portion of fig. 2 from a. Magnified 80 
diameters. 
Fig. 4. Similarly enlarged view of a portion from fig. 2 b. Magnified 80 diameters. 
Fig. 5. Horizontal section of the lower or membranous laminae of the same scale. 
Magnified 70 diameters. 
Fig. 6. Horizontal section of the middle layer of the same scale. Magnified 100 
diameters. 
Fig. 7. Superficial aspect of a small portion taken from fig. 1 c. Magnified 25 dia- 
meters. 
Fig. 8. Corresponding view of a portion removed from fig. 1 d. Magnified 25 dia- 
meters. 
Fig. 9. Vertical section of part of the anterior portion of the scale of a Carp, made 
parallel to the mesial line. Magnified 160 diameters. 
Fig. 10. Horizontal section of the uppermost of the membranous laminae of the scale 
of the Perch. Inverted and magnified 200 diameters. 
Fig. 1 1. Vertical section of the posterior margin of the scale of the Perch. Magnified 
75 diameters. 
Fig. 12. Horizontal aspect of the corresponding portion of the same scale. Magni- 
fied 50 diameters. 
