DEVELOPMENT OF FISHES 49 



with the development of the tail of a species of stickle- 

 back. It is a familiar fact that the tail of a shark or dog- 

 fish, members of a very ancient group, is externally 

 markedly unsymmetrical, there being a large upper lobe 

 into or towards which the vertebral column is bent. 

 The tails of the more modern bony fishes, e.g., herring, 

 mackerel, and stickleback, are externally symmetrical, 

 and the backbone appears to end off where its upper and 

 lower lobes begin. A study of the development of the 

 latter shows, however, that this kind of tail is merely an 

 improvement of the older type, and that internally it is 

 markedly unsymmetrical. 



11. " On the Dermal Armour of Jacare and Caiman, 

 with Notes on the Specific and Generic Characters of 

 Recent Crocodilia" (J. Linn. Soc. (Zool.), iv, i860, 

 pp. 1-28. Read February 15, 1859. Sci. Mem., ii, xvi, 

 p. 286). — The research embodied in this memoir was 

 led up to by previous work upon extinct crocodilians. 



12. " On the Anatomy and Development of Pyro- 

 soma" (Trans. Linn. Soc, xxiii, 1862, pp. 193-250. 

 Read December 1, 1859. Sci. Mem., ii, xvn, p. 313). 

 — This classical monograph deals with a floating colonial 

 tunicate or ascidian, which is one of the sources of the 

 phosphorescence of the sea. The subject is worked out 

 in detail, and alternation of generations established for 

 the life-history. 



