J. K. Di'KKDKN 18:] 



TABLE VIII. 

 Xutnbf'r of Scale's in Tarmjmlal ScnlfUation. 

 A. ContinuoM* : 



Table VIII show, the breaks represent a deHnite loss of scales. Taken 

 along with the other facts of degeneration in the foot, the losses are 

 without doubt to be regarded as the first evidence of degeneration in the 

 middle toe of the ostrich, the first, second and fifth having already disap- 

 peared and the small fourth being well on the way. The breaks evidently 

 represent independent unit characters, retrogressive mutations, in course 

 of introduction within the whole race, the process having gone a little 

 further in the northern ostrich than in the southern. 



In all ostriches the tarsal scutellation is now distinct from that over 

 the small toe, only 8 to 10 scales occurring distally (Text-fig. 2). Com- 

 parison with other birds would, however, lead one to expect that the 

 two series were originally continuous', as they are still in the great 

 majority of ostriches with regard to the middle toe. 



Breeding experiments prove that the breaks between the tarsus and 

 middle toe are germinal in their nature. Where no break occurs in 

 either of the parents the progeny also show no loss of scales. Thus in 

 13 cross-bred chicks from a southern cock and a northern hen, both 

 with a continuous scutellation, no loss of scales occurred. When how- 

 ever one of the parents bears a break and not the other, then, as indicated 

 below, approximately one-half of the chicks displays the loss, proving 

 that the factor for the break is dominant but that the germ plasm is 

 simplex or heterozygous with reference to it. 



' At extensive series of birds' feet is shown on p. 425 of Sedfiwicks, Students' Test-book of 

 Zoology, Vol. ii. 1905, where however the Kcutellation of Stnithio camelim is erroneously 

 represented, i\\o scales of tlip small to«' boinp depicted as continuous with those of the 

 tarsus. 



