94 SOME SUGGESTIONS FOR BIRD STUDY. 



Exercises in description of eggs where these are available 

 form excellent tests of the pupils' powers of colour descrip- 

 tion. The eggs should be drawn and coloured. Where 

 clay modelling is practised this might be attempted. The 

 models should be covered with white enamel paint, and the 

 ground colour and markings painted over this. 



STUDY OF AN EGG IN DETAIL. 



Take an ordinary fowl's egg. Note the following points. 

 The shape ; it is quite distinctive. We find it described in 

 books as "ovoid, 5 ' that is, egg-shaped. Usually an egg has 

 one end broader than another, but some eggs, e.g. those of 

 some owls, tend to be almost spherical. The shell consists 

 of carbonate of lime, phosphate of lime, and animal gluten. 

 Some eggs are smooth in texture, e.g. those of aquatic 

 birds. Such eggs do not wet readily. A fowl's egg is 

 coarser grained. The shell is porous, admitting the passage 

 of oxygen inward and of carbon dioxide outward for the 

 respiration of the growing bird. Evaporation of the con- 

 tents also goes on through the pores after the egg is laid. 



The size of an egg generally has some relation to the 

 size of the bird laying it, but there are some interesting 

 cases. The cuckoo, a bird about twelve inches long, lays a 

 small egg scarcely an inch in length. The guillemot, a 

 bird about the size of a rook, has an egg about three inches 

 in length, whilst the apteryx, a flightless nocturnal bird of 

 New Zealand about the size of a small fowl, lays an egg 

 about the size of that of a goose. 



What is the weight of an ordinary hen's egg ? About 

 two ounces, but pupils might be asked to guess by testing 

 in the hand. 



Within the egg, just beneath the shell, lie the shell 

 membranes. Pupils will be familiar with one membrane, 

 perhaps not so familiar with the fact that there are two. 

 Demonstrate at the broad end of a hard boiled egg the two 

 membranes, one against the shell, the other lying against 

 the white of the egg. Note the "air space" between. 

 Shell and membranes protect in part what lies within from 



