J. E. DUERDBN 193 



tion generally, and also as to the diverse results which may be obtained 

 from the same factors when in a changing state. From a wholly 

 different point of view it fully supports Morgan's contention as to possible 

 discrepancies between somatic expression and factorial condition ; it may 

 also enable us to understand how an appearance of somatic continuity 

 can. be conferred though the germinal changes are discrete and sequen- 

 tial. At any rate when factors are in a variable state it must create a 

 strong sense of insecurity in the expressions obtained. 



DESCRIPTION OF PLATES. 



PLATE V. 



Fig. 1. Outer surface of wing with plumes clipped from quills. South African ostrich. 



Fig. 2. Under surface of terminal part of wing. The bastard wing is just visible above, 

 the second finger with its claw extends to the tip of the wing, while the third finger 

 projects freely from the general surface below, its tip rounded and callous. Near the 

 third finger an irregularity in the row of under-coverts and of wing-quills occurs, the 

 two additional feathers belonging to the third digit. 



PLATE VL 



Fig. 3. Three young ostrich chicks showing upper part of leg covered with natal down. 



Fig. 4. Under surface of ostrich to show the featherless condition of the legs, the lateral 

 apteria, and the sternal and pubic callosities. The pits of the sockets from which the 

 feathers have dropped out can still be seen on the legs, and also one or two persistent 

 feathers. The bird is about eighteen months old and the white ventral feathers are 

 not yet wholly replaced by the black feathers of the adult cock plumage. 



Fig. 5. Wing of embryo chick (left), about fourteen days' incubation, showing the first 

 three digits. The third finger below is much shorter than the second and gradually 

 becomes proportionately smaller. 



Tarsus and foot of embryo chick (right), about fourteen days' incubation. The third and 

 fourth toes are of nearly equal size while the second appears as a slight projection on 

 the left. 



Fig. 6. Tarsus and foot of young chick with scutellation at about same stage as that in 

 Fig. 7 and like e in Fig. 8. 



