PKOTECTIVE KESEMBLANCES IN VEKTEBRATA 69 



of the surface swimming fish, Leptocephalus, is in- 

 creased in this way.^ 



Protective Resemblances among Marine Animals 



Before leaving this part of the subject I must 

 allude to Protective Eesemblances among marine 

 animals. Although large numbers of isolated cases 

 are understood, the principles of colouring in marine 

 forms have been very incompletely worked out. The 

 difficulties are far greater than in land animals, be- 

 cause it is often nearly impossible to observe the 

 species in their natural environment, and it has 

 been already shown that this is essential if we are fully 

 to understand the meaning of all details in their 

 appearance and attitudes. It is, however, very satis- 

 factory to know that the whole subject of the colouring 

 of marine mollusca is being undertaken in a syste- 

 matic manner by Mr. W. Garstang,^ assisted by all the 

 appliances of the laboratory of the Marine Biological 

 Association at Plymouth. 



Protective Resemblances among Marine Mollusca 



E. S. Morse has shown, contrary to Darwin's 

 opinion,^ that the appearances of many mollusca 

 are such as to afford concealment. An extremely 



' E. Ray Lankester, ' On the Distribution of Haemoglobin,' Proc. 

 Boy. Soc. No. 140, 1873. 



2 Journ. Mar. Biol. Assoc, New Series, vol. i. No. 2, Oct. 18S9, 

 pp. 173 et seq. 



^ Descent of Man, vol. i. p. 816. 



