244 THE BIOLOGY OF BIRDS 



germ-cells which do not take any part in body-making, but 

 are set apart at a very early date, continuing, as it were, intact 

 the tradition of the fertilised egg-cell from which they and 

 the body-cells arise. The old question : Does the hen make 

 the egg, or does the egg make the hen ? was, like many 

 similar questions, a false alternative. The fertilised egg- 

 cell gives rise to the hen and the egg-cells thereof, or to the 

 cock and the sperm-cells thereof. This is the general idea 

 of the continuity of the germ-plasm which Weismann and 

 Galton first made clear, though it had been in the minds of 

 some of their predecessors. Galton 's view was that the 

 ovum was like a nest of organic units, to which in their 

 entirety he applied the word stirp. He regarded it as directly 

 derived from a previous nest, namely, from the ovum which 

 gave rise to the parent. He maintained that in development 

 the bulk of the stirp grew into the body — as every one allows 

 — but that a certain residue was kept apart from the develop- 

 ment of the " body " to form the reproductive elements of 

 the offspring. Thus, he said, in a sense the child is as old as 

 the parent, for when the parent is developing from the ovum 

 a residue of that ovum is kept apart to form the germ-cells, 

 one of which will become or may become a child. Or, as 

 Weismann put it : "In each development a portion of the 

 specific germ-plasm contained in the parent egg-cell is not 

 used up in the construction of the body of the offspring, but 

 is reserved unchanged for the formation of the germ-cells 

 of the following generation." Such in general terms is the 

 origin of the gonads. 



Is there any explanation of the suppression of the 

 right ovary and oviduct ? Snakes show a tendency to 

 suppress the left lung and we can interpret this as an 

 adaptation to the narrow space of the elongated body- 

 cavity, but why do female birds suppress the ovary and 

 oviduct of one side, always the same side ? Perhaps for 

 a flying creature it would be disadvantageous to have two 

 ovaries with relatively large and heavy eggs. Perhaps 

 it would be similarly disadvantageous to have two oviducts 

 with relatively large and hard-shelled eggs. It may be 



