1908. The British Association in Dublin, 225 



defensive organs," and that their services arevahiable against 

 " encrusting organisms, including other species of Pol3-zoa ; 

 . . indeed, the enemies against which a polyzoon has to 

 provide are probably in a special degree the members of its 

 own class." Attention was called to the extreme variability 

 of the avicularia among the Polyzoa, and the difficulties raised 

 by this variabilit\'. " What conclusion can we draw from the 

 association in one and the same colony of the vicarious type 

 of avicularium with adventitious avicularia of the most special- 

 ized description ? How can we explain the fact that each 

 kind of avicularium occurs in certain species, but not in all 

 the species, of many distinct and not specially related genera? 

 And lastly, what is the significance of the fact that certain 

 species of a genus which is normally provided with avicularia 

 may be totall}- destitute of these organs ? " It is not surpris- 

 ing that Dr. Harmer, meditating on these problems in the 

 Cambridge of the twentieth century, suggests "that some of 

 our difficulties might be removed by appealing to the results 

 obtained by workers on Mendelian inheritance . . . that 

 the perplexing occurrence of vicarious avicularia in some of 

 the colonies of certain species may be interpreted as a rever- 

 sion due to the combination of two or more allelomorphs 

 that may not have occurred together in the parental forms." 



The meetings of Section D were, on the whole, of very 

 great interest. Abstracts oi papers dealing, directly or in- 

 directly, with Irish questions are given below. Perhaps the 

 most striking feature was a joint discussion with Section K 

 on the "Determination of Sex," on Mondaj^ 7th September, 

 opened by Mr. L- Doncaster, and continued by Miss N. M. 

 Stevens, Mr. W. Heape, F.R.S., and Professor W. Bateson, 

 F.R.S. Mr. Doncaster, from breeding experiments with the 

 common Magpie Moth {Abraxas grossii lariat a\2ivA its variety 

 lacticolor, concludes that " sex determinants behave as Men- 

 delian characters, maleness and femaleness being allelomor- 

 phic with one another, and femaleness dominant. All 

 females are heterozygotes, carrying recessive maleness, and 

 producing male-bearing and female-bearing eggs in equal 

 numbers ; all males'are homozygoteS; carrying only maleness? 

 and producing only male-bearing spermatozoa." This theory 

 was supported by the remarkable researches detailed by Miss 



A 5 



