110 THE ZOOLOGIST. 



or may not be cracked by the blow." This is true ; but if the nut is broken 

 by the bird, then it has been hacked. The Nuthatch habitually breaks 

 nuts. — O. V. Aplin (Bloxham, Oxon). 



Note on the Weight and Specific Gravity of some Common Eggs. — 

 It is with diffidence and some hesitation that I record the followiug details 

 of some few eggs that I have weighed, and of which I have also taken the 

 specific gravity, during the past egg season. It is very probable that the 

 average weights of the eggs of the commoner species have been already 

 recorded, and it is difficult for the dweller in the country, with few oppor- 

 tunities of consulting the literature of a subject, to be aware of what 

 has been done. He is therefore restricted to the recording of facts of 

 observation honestly, and with the greatest care and accuracy of which he 

 is capable ; and he must leave to those with larger material and better 

 opportunities for reference at their command the deductions which may be 

 drawn from the facts which he has put on record. This is perhaps the less 

 to be regretted when one recognises the danger, so difficult to avoid, of 

 being more or less unconsciously influenced by the exigencies of an imper- 

 fectly formed theory while recording the facts which may or may not 

 support it. 



The weighings given below were made on a chemical balance turning 

 with -001 gramme, and may be taken as accurate. The specific gravities 

 must not be taken as absolute, but are accurate when compared inter se, 

 the source of error being the weight and specific gravity of the fine india- 

 rubber ring and thread used to support the egg while being weighed in 

 water. It would doubtless have been desirable to have weighed a clutch of 

 each species, but this was impossible in the time at my disposal ; in two 

 instances, however — Tardus merula and Vanellus vanellus— three eggs 

 from the same nest were dealt with, and it will be seen that the variation 

 in weight and specific gravity is very noticeable. Again, if the weights of 

 eggs of the same species are to be compared, they should perhaps be 

 weighed at the same age, though whether any appreciable change takes 

 place until after the bird has begun to sit regularly is doubtful. In all the 

 cases given, except three — Alauda arvensis, J. phragmitis, and Sylvia 

 Sylvia — the eggs were taken before the whole clutch was laid, and in none 

 except the last named had the process of incubation apparently com- 

 menced. With these exceptions, however, the specific gravities may be 

 taken as comparable. It was, of course, to be expected that the weights of 

 eggs even from the same nest would vary, but the considerable variation in 

 the specific gravities was unexpected, and may perhaps be partly due to a 

 varying amount of salts in the shell and contents of the egg, caused by a 

 greater or lesser amount of lime in the diet of the parent during the time 

 the eggs are being matured ; or it may possibly be partly due to difference 



