BIRDS' EGGS 



255 



H- 



-n-P 



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ference facilitated by the development of a grooved muscular 

 organ or penis, which has its antecedent in Crocodilian and 

 Chelonian reptiles. 



This is not continuous with the 

 male ducts as it is in mammals, but 

 rises from the wall of the cloaca. 

 It is practically confined to the 

 Ratitae and to duck-like birds, but 

 a rudimentary one occurs in a few 

 Carinatae. It is well-developed in 

 the Great Tinamou and rudimen- 

 tary in Crypturus, both members of 

 the family of Tinamous which many 

 authorities would refer to the Ratitae. 

 Gerhardt (1908) has described a 

 well-developed penis in the Crested 

 Curassow, Crax alector, and Tschudi 

 reports the same for the Guan,Pe«e- 

 lope abourri, which belongs to the 

 same Gallinaceous family of Cracidas. 



It is of some interest to find that 

 there is sometimes asymmetry in 

 the testes as well as in the ovaries. 

 Raymond Pearl (1908) notes that in 

 adult doves and pigeons, if quite 

 healthy, the right testis is larger fig. 40 

 than the left in a very high per- 

 centage of cases. The left testis, in 

 a high percentage of cases, is abso- 

 lutely longer and thinner than the 

 right, more nearly approaching the 

 shape of the persistent (left) ovary. 

 In disease — particularly in tuber- 

 culosis — the testes undergo extreme 

 atrophy (often 90 to 95 per cent.) ; 

 the reduction is greater in the right 

 testis than in the left. In hybrids the normal size relations 

 of the two testes are much disturbed. 



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Three forms of 

 spermatozoa in birds. H., 

 the head, containing the 

 chromosomes ; T., the tail, 

 which is locomotor in 

 function; m.p., a middle 

 piece in which there lies a 

 minute centrosome ; f., a 

 delicate fringe on the head. 

 It must be noted that a 

 hundred spermatozoa can 

 swim about in a drop of 

 fluid susfiended from the 

 head of a pin ; they are 

 extremely minute cells. 



