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pallid variation ; melanism or darkening ; heteropoecilisms or spots ; 

 gynandrochroniism or male assuming the female form ; and hermaphrodism 

 or the combination of the two sexes in one individual. The pinncipal 

 groups of orthopoecilic varieties are — polymorphism, or numerous variations 

 rendering the type uncertain ; topomorphism, or varieties due to habitat ; 

 atavism, or reversion to an earlier type ; dimorphism, or two static 

 conditions of the same species ; and horeomorphism, or seasonal variations. 

 After defining a type, the theories of Lord Walsingham on melanism, and 

 of Mr. Dupre were discussed, and the facts inconsistent with each theory 

 pointed out. With some diffidence, the lecturer ventured to name the result 

 of some of his own experiments, which induced him to think that possibly 

 humidity might be an element in some of these changes. An interesting 

 discussion followed. 



Meeting held in the Library of the Philosophical Hall, Park Eow, 

 April 1st, 1889. John Stubbins, F.G.S., F.E.M.S., Vice-President, in the 

 chair. 

 Exhibits : — 



The chairman called attention to a fine collection of Indian Ferns and 

 Mosses beautifully arranged and mounted, retaining to a remarkable 

 extent their natural colour, exhibited by Mr. James Moorhouse. 



Mr. Edgar E. Waite exhibited and described a collection of birds' nests. 

 In the course of his remarks, the speaker stated that although this was an 

 important branch of ornithology comparatively few students in this section 

 of natural history collected the nests of birds. Mr. Waite, however, ex- 

 hibited a very representative collection, and so illustrated the most 

 important peculiarities of nest construction. This was made still more 

 complete by the exhibition of sketches of other nests which will not admit 

 of being removed in their entirety, e.g., those of the Sand Martin, King- 

 fisher, and similar nesters. The speaker called attention to a great variety 

 of nests, and in order to render the subject more comprehensive, proceeded 

 to classify them according to their various peculiarities, which classification 

 he remarked was of the rudest description, having nothing in common 

 with the systematic classification of the birds themselves, the following are 

 the groups into which the subject was roughly divided, together with the 

 representative, illustrated either by actual specimens or by drawings : — 

 Weavers — Baltimore Oriole, Baya Weaver Bird, Crested hangnest, &c.; 

 Tailors — Orthotomus autorius ; Felters — Penduline Tit, Pinc-pinc ; 

 Basketers — Magpie, &c.; Plasterers — Swallow, Martin, &c.; Excavators — 

 Sand Martin, Woodpecker ; Ground Builders — Flamingo, Megapodes ; 

 Non-nest Makers— Guillemot, Eazorbill ; Parasites— Cuckoo, Cowbird 

 {Molothrxis pecoris). 



Mr. J. W. Addymau, B.A., exhibited a number of Diatoms, and gave a 

 short account of the variety of forms, structure, and life-history of the 

 group. 



