Prof. J. Wood-Mason on a Viviparous Caddis-jJy. 139 



assumes the fundamental fact on which the theory of segre- 

 gation rests. All that is wanting is its recognition as a 

 universal principle on which all permanent divergences, 

 whether varietal or specific, necessarily depend. In the 

 formation of domestic variations it is fully recognized ; for he 

 says, " It is only by isolation and pure breeding that any 

 specially desired qualities can be increased by selection " 

 (p. 99). If experimental biology shows this to be a constant 

 law, is there any good reason for not applying it in the general 

 theory of organic evolution? Seeing it is admitted that arti- 

 ficial selection, unaided by isolation, is of no avail in pro- 

 ducing divergent races, how can it be claimed that natural 

 selection, unaided by isolation, is of any avail in producing 

 varieties and species? Again, as in domestication the segre- 

 gate breeding of other than average forms always produces 

 divergence, have we any reason to doubt that, when the same 

 process takes place in the grouping of organisms in a natural 

 state, the result will also be divergence ? 



The discrepancies to which I have referred are, it seems to 

 me, due to deficiencies in the theory which Mr. Wallace 

 maintains in common with many others. These problems 

 tiiat drive the exclusive utilitarian into various inconsisten- 

 cies, can, I am convinced, be consistently explained by the 

 theory of Divergence through Segregation. 



26 Concession, Osaka, Japan. 



XV. — On a Viviparous Caddis-fly. By J. Wood-MaSON, 

 Superintendent of the Indian Museum, and Professor of 

 Comparative Anatomy in the Medical College of Bengal, 

 Calcutta. 



Some years ago, while studying a series of transverse sections 

 through the body of a Trichopterous insect I had captured at 

 the dinner-table lights, I noticed that the abdomen was 

 crammed from end to end with partially developed ova. On 

 the 25th October last I caught a second specimen of the same 

 species, which also proved to be a gravid female. Remem- 

 bering my former observation, and having often observed 

 that gravid females of the viviparous forms of Muscidaj bring 

 forth their young on falling accidentally into the spirit of the 

 dissecting-dish, I threw the insect alive into a liqueur-glass of 

 whiskey that happened to be ready at hand. The moment that 



