299 



of the sliell contrasting the thin shell of Duck and the 

 thick shell of the Aepyorius, a large extinct bird of 

 Madagascar, giving the Ostrich's as an intermediate. 



The next card contains an egg of a Tern to show the 

 various shades the one and the same pigment produces, 

 depending upon the depth at which the pigment is formed. 

 Superficial pigment dark and sharply defined, deep pigment 

 light and more or less bliirred. 



2. — Number of eggs i^aid : 



The eggs laid in one nest which are sat upon together 

 and hatched about the same time are called a clutch, their 

 number though tolerably uniform in each species, vary 

 greatly in different species. 



Some have only one, others two, majority four or five. 

 Higher numbers are less common, but eight and twelve are 

 frequently found among Ducks and Rails, and even more 

 among some game birds. 



Specimens illustrating the above facts are : 



(a). Single egg of Manx Shearwater and Razorbill. 



■{d). Two eggs in Black Guillemot, ySwift and P-ing Dove. 



(c). Three eggs in Oyster Catcher. 



(d). Four eggs in Golden Plover and Common Sandpiper. 



'((f). Five eggs in Kestrel and Robin. 



(/). Higher numbers in Long-tailed Tits and Red-legged 

 Partridge. 



3.— Form : 



In form eggs vary from almost spherical to different 

 modification of elliptical or oval. The latter form in which 

 one end is smaller and more pointed than other is the 

 most frequent, and distinguishes eggs of birds from 

 reptiles. If there are man3' eggs in the nest it is obvious 

 that the conical form makes close packing more easy. 

 Where only two eggs aie laid they are seldom conical. 

 Eggs having a pyriform or pear shape are mostly those 

 of birds which lay four in a nest and are large in pro- 

 portion to size of bird. Their pointed ends being turned 

 inwards, they occupy as little space as possible and thus are 

 more easily covered by the brooding parent. 



