35O GEORGE W. BARTELMEZ. 



p. 12) as he was the first to discuss axis angles was the first to 

 record an inversion. He observed only one and suggested that it 

 might have resulted from the cracking of the shell before incuba- 

 tion. It is evident from this that he did not appreciate the funda- 

 mental nature of the relation between embryo and principal egg 

 axis. Subsequent workers, perhaps on this hint of v. Baer's, have 

 presented evidence that the axis angle may be changed by experi- 

 mental means. Thus Blanc (1892), Fere (1897 and later), 

 Ferret et Weber (1904) and others have reported not only an 

 increase in the number of extreme variations but also an increase 

 in the number of inversions after poisoning the embryo or after 

 interference with the secondary envelopes. While it is possible 

 that an injured embryo may grow irregularly and so change the 

 original direction of its axis (Fere, 1900) it is highly improbable 

 that it could become inverted. Most of these workers have not 

 adequately determined the normal range of variability of their 

 material. As has been said, the variability may in certain cases 

 be much greater in the hen than in the pigeon. Professor A. P. 

 Mathews tells me that as a student he planned similar experi- 

 ments but abandoned them when he realized the extent of the 

 normal variation in the hen's egg. 



It is interesting to note in this connection that the earlier 

 editions of Foster and Balfour's text-book gave the relations 

 here termed "inversions" as the normal ones for the hen. As 

 Balfour wrote this section of the book it may have been based 

 upon his own observations or it may have merely been an acci- 

 dental error. Dal ton (1881) reported 12 hen's eggs inverted 

 out of 100 while Duval (1884) found only one among 166, 

 Rabaud (1908) 12 in 98 and the writer 33 in 100. For the pigeon 

 on the other hand I reported (1912, p. 301), four cases among 

 over 600 observations by Drs. Blount, Patterson and myself. 

 The present study has thrown some new light on the question. 



Inversions are very rare in pigeon eggs. I have studied eggs 

 from about 90 pigeons; while many of them came from the five 

 birds mentioned above, between two and twenty have been 

 obtained from each of the others. Among all these only two 

 birds, no. 4 and no. 5 laid inverted eggs. No. 4 laid two among 

 94, no. 5 six among 102 eggs. In pigeon no. 5 the axis angles was 



