282 SOME RESULTS OF OSTRICH INVESTIGATIONS. 



ostrich wing far different from that of to-day. The only hmita- 

 tions imposed will be in connection with those ancestral characters 

 the factors for which have altogether disappeared from the germ 

 plasm. No selection can bring back these. We can only 

 construct from the material which is left; much, however, has 

 gone for ever. 



Pineal Patch. 



In all ostrich chicks, on hatching, a small, bare, oval patch 

 occurs towards the back of the head. (Fig. 4.) As the chick 

 grows older, it tends to be hidden by the downy and bristly 

 feathers which constitute the covering of the head, but even in 

 the adult it can always be observed by turning the feathers aside. 

 The area is somewhat darker coloured than the rest of the skin, 

 and never bears feathers. Dissections reveal that it is situated 

 over the part of the brain known as the pineal body, which, in 

 the ostrich, is a rather large oval structure occupying the trian- 

 gular space formed by the two cerebral hemispheres and the 

 cerebellum. During the com-se of development, the patch appears. 



^■;|^. 





Fig. 4. 



even more conspicuous than in the newly-hatched chick, and is 

 always darkly pigmented. At a certain stage it has been found to 

 be raised a little above the general surface as a black vesicular 

 swelling. 



Embryological studies have not yet been carried out to 

 determine the microscopic structure, nor how far the superficial 

 area is connected with the pineal stalk below. On the skull itself 

 no indication appears of any connection ; so that if a prior attach- 

 ment occurs it must be severed at an early stage of development. 

 There can be no doubt, however, of the association between the 

 oval area and the pineal body, and that the former may justly 

 be regarded as a pineal patch. Similar pineal structures are 

 frequently found in the Reptilia, where they often take on the 

 character of sense organs, particularly of a visual nature, the most 

 familiar being the pineal eye in the New Zealand lizard, Sphcn- 

 don. They are also known among the amyhibia. 



Apparently the ostrich is unique among birds in having the 

 jiineal patch, and its presence serves to emphasize the generally- 

 accepted close relationship of the birds and reptiles. It also 

 •confirms the closer relationship which the ostrich bears to the 



