275 

 DIMORPHISM IN THE EGGS OF 

 TURDUS MUSIC US. 



C. J. PATTEN, M.A., M.D., Sc.D. 

 Sheffield. 



Being recently engaged in research into some points in avian 

 embryology I solicited from gardeners, fruit-growers, and others, 

 donations of eggs of some of our common species. A liberal 

 response brought to me a number of eggs of the House-Sparrow, 

 Blackbird and Song-Thrush, and in more limited numbers eggs 

 of several other species. Some interesting variations in the shells 

 came under my notice, especially in the case of the House- 

 Sparrow and Song-Thrush. In the present paper I will deal 

 only with the latter. I need merely give a passing notice 



8. 

 Dimorphism in the Eggs of Tardus musicus. 



No. 4 is entirely devoid of spots. In Nos. 1, 2 and 3 the spots, and more especially 

 the large blotches, are reddish-brown. In No. 3 there is, however, a large blackish blotch 

 in addition. The unspotted egg (No. 4) is the longest ; No. 2 comes next, both of these eggs being 

 more pointed than the shorter ones Nos. 1 and 3. The measurements are as follows : — No. 1 — 2-8 cm. 

 by 2-2 cm. ; No. 2—29 cm. by 22 cm. ; No. 3—2-8 cm. by 21 cm. ; No. 4—3 cm. by 22 cm. It may, 

 therefore, be observed that in breadth the eggs are practically of the one measurement. 



regarding variation in size in which in three clutches each egg 

 measured only i'8 cm. or 7 mm. below the average as given by 

 Saunders (' Man. Brit. Birds,' Sec. Edit., p. 4), while regarding 

 variation in the distribution and size of the spots, I may men- 

 tion that in two clutches they were exceedingly small, and 

 wholly confined to the pointed ends. 



I now wish to refer in some detail to a clutch in which one 

 egg was entirely devoid of spots. I do not place so much im- 

 portance in the discovery of a Thrush's egg without spots ; 

 it is generally known among ornithologists that such cases are 

 by no means rare, but when the contents were examined in 

 conjunction with the shell, some interesting points cropped up. 



1909 Aug. I. 



