AS AN INDEX OF AGE. 17 



individuals of the same species, but on different regions of the body on the 

 same individual Owing to this variation he regards Agassiz's division into 

 cycloid and ctenoid as of little value. 



The next work which I have to notice is a lengthened and interesting paper 

 by Baudelot, in three parts.* 



Part I. is concerned with a historical review of the literature relating to 

 scales previous to the year 1873, of which I have made ample use in the 

 foregoing pages. Part II. contains a detailed study of a certain number of 

 types of scales, considered from the point of view of structure and develop- 

 ment. Part III. has a number of facts on the value of the characters found 

 in scales in relation to classification. 



Part II. consists of two sections, of which the second section gives a 

 synthetic summary of the facts propounded in the first section. 



In Section I. he treats of the following : — 



Analytical study of types of scales. 



1. Perca Jftiviatilis, with eight figures. 



2. Phoxinus Icevis, with one figure. 



3. Esox lucius, with two figures. 



4. Clupea harengus, with one figure. 



5. Anguilla vnhjaris, with five figures. 



6. Ophidium harhatum, with two figures. 



7. Gadus merlayigus. 



8. Cyprinus carpio, with eight figures. 



9. Pleuronectes solea, with five figures. 



10. Tliynnus vulgaris, with seven figures. 



11. Mugil capito, with eleven figures. 



12. Hypostomum, with fourteen figures. 



In this analytical study of the foregoing types of scales, he devotes much 

 attention to the corpuscles of scales. 



In the second and synthetic section of Part II. he treats of the following: — 



1. The connection between the scales and integument. 



2. The form of scales and their mode of orientation. 



3. The size of scales. 



4. The ridges on scales. 



5. The spines on scales. 



6. The grooves on scales. 



7. The perforating canals in scales. 



8. The internal lacunae of scales. 



9. The focus or centre of growth. 



10. The tissue of scales. 



11. The formation and growth of scales. 



1. The connection bettveen the scales and integument. The scales of 

 cycloid and ctenoid fishes are usually contained in small dermic sacs, 

 and are more or less visible to the exterior; but in some cases they are 

 not so, being deeply buried in the skin (Anguilla, Oi)hidium, Lota, etc.). 



* Baudelot, 1873. 



NEW SERIES.— VOL. VII. No. 1. B 



