Vol. xxxvi.] 22 



of exceptions ; most Swifts lay two eggs^ yet among our 

 Common Swift and other species three are not very rare, 

 while some species lay mostly three eggs, so that this rule 

 also is not without exceptions. In some cases, as in the 

 Rough-legged Buzzard, the number of eggs in the clutch 

 varies according to the abundance of food in different years ; 

 in Passer simplex the clutch varies from one to five eggs ! 

 The texture of the shell is much neglected by collectors, 

 and so is the comparative thickness, though both characters 

 are generally fairly constant, and in some cases important — 

 I will mention only the comparative great thickness of the 

 egg-shell of Cuculus canorus — but, on the other hand, the 

 same texture occurs in eggs of widely different families ! 



I therefore conclude that characters of the egg-shell 

 cannot decide the systematic position of any bird against 

 other factors, but that they can give very useful hints and 

 can corroborate views gained from anatomy, osteology, 

 pterylography, structure of bills, feet, etc. 



I might here repeat what I said twenty-five years ago : 

 Nowadays the words oology and oologists sometimes pro- 

 duce unkind thoughts and words, suggesting the plunder of 

 nests and extinction of rare birds, or, what is still worse, of 

 work Avithout any scientific value. This happens because 

 the public does not differentiate between an egg-collector 

 and an oologist. Of course the collector likes to be called 

 an oologist, while this name should only be applied to those 

 who study their eggs and make their studies known to the 

 scientific world. The fact, however, is that the number of 

 real oologists is very small, while that of egg-collectors is 

 very large. On the other hand, if one wishes to study 

 Oology, one is, in most cases, obliged to make a collection, 

 because very few museums possess a really large collection, 

 containing many reliable eggs of foreign birds as well. 



But the study of eggs is indispensable, quite as indis- 

 pensable as that of the caterpillars is for a lepidopterist, or 

 that of the seeds for a botanist. We cannot say that we 

 know birds if we are only acquainted with their structure 

 and feathers. Moreover, it often opens wide vistas and 

 assists us sometimes in classification. 



