1894. NOTES AND COMMENTS. ii 



The Colours of Birds' Eggs. 



The value to be assigned to the colour of eggs in classification, 

 is a point in which the personal equation plays an enormous part. 

 Probably no two ornithologists would agree about many of the most 

 common cases. Some of the difficulty, no doubt, is due to our 

 ignorance of the natural processes by which the colours and markings 

 are produced. Dr. Heinrich Wickmann has recently published, at 

 Miinster, a pamphlet of sixty-four pages on the origin of the colouring 

 of birds' eggs. He states that the egg-shells of most birds consist of 

 three parts. There is the inner elastic and fibrous layer, with 

 which we are all familiar, and which is double, the middle calcified 

 layer, and a thin organic cuticle, which is not found in all eggs. In 

 coloured eggs the ground colour is to be distinguished from flecks of 

 colour. These latter extend only a very small distance into the 

 calcified layer, while the ground colour penetrates to the innermost 

 part of the shell. But white eggs, says this author, are not unpig- 

 mented and white merely because chalk is white. There are separate 

 white pigments present, and an egg of which the white ground colour 

 is due to one pigment may be flecked with white spots of another 

 white pigment. 



He agrees with Kutter that the colours are deposited while the 

 egg is in the uterus, before it has reached the cloaca, and gives a 

 list of birds, including the duck, the heron, partridge, crow, falcon, 

 blackcap, cuckoo, nightingale, and snipe, in which he has found 

 actually in the uterus an egg with the complete normal colouring. 

 Further, he rejects all former hypotheses as to the place of origin of 

 the colours, and comes to the conclusion, although on what seems to 

 us insufficient evidence, that all pigments are formed in the ovary 

 shortly after the egg has entered the tube, and are discharged into the 

 tube, down which they follow the egg to the viterus. He believes that 

 the origin of the colouring matters is to be found in the blood, which 

 undergoes katabolic changes during the formation of the corpus luteum. 

 The different colours of the eggs, even of nearly-allied birds, he 

 explains in a somewhat cavalier manner, by attributing them to 

 slight differences in the chemical constituents of the blood of these 

 animals. We do not think that Dr. Wickmann has left nothing for 

 future investigators, and we regret that he has given insufficient 

 details of his methods of investigation ; but he has made a notable 

 contribution to oology. In a concluding paragraph, the writer says, 

 with some pride, that all the work was done in his private room, and 

 that he has to thank no professor nor institution for aid. 



Tadpoles. 



The day has gone by for accepting Tadpoles, or indeed any 

 larval forms, as simple survivals of an ancestral condition. We 

 know now that the larvae of many sponges echinoderms, marine 



