THE EGG 



of the surface cells. This is still not out of the question, in 

 spite of the relatively small size of the cilia as compared to 

 the eggs — about in the proportion of an eyelash to an orange 

 (Plate X, jE). With a bunch of eyelashes or something similar, 

 for example a tiny camel's hair brush, it does not take much 

 effort to roll along an orange floating in water, as the eggs 

 float in the fluid contents of the oviduct. 



This supposition, however, has its weak points. In the first 

 place there are animals in which the oviduct is not provided 

 with cilia throughout its entire length. In the second place, 

 there is a remarkable fact which cannot easily be explained 

 on the basis of ciliary transport, namely that the oviducts of 

 different species of animals are of very different lengths, and 

 yet with only a few known exceptions, the eggs make their 

 journey through them in about the same time, reaching the 

 uterus in 3 to 3% days. The oviduct of the sow is about forty 

 times as long as that of the mouse, therefore the eggs must 

 travel forty times as fast. The cilia, however, certainly do not 

 beat that much more rapidly. 



What is more, the cilia beat with more or less uniform 

 motion, while the eggs do not travel at uniform speed. A 

 former colleague of mine. Dr. Dorothy Andersen, once col- 

 lected at a packing house a very large number of oviducts 

 of swine containing eggs. She cut up each one into 5 segments 

 and examined each segment separately to see whether it con- 

 tained eggs. She found that it is common to find eggs in the 

 middle segments, but rare to find them in the first and in the 

 last parts of the tube — in other words, the eggs are rushed 

 through the first fifth, transported very slowly through the 

 middle stretch, and then hurried through the last part into 

 the uterus. A similar and even more accurate observation 

 has since been made in the mouse (W. H. Lewis and Wright). 



All these difficulties lead us to suppose that the eggs are 

 really transported by contractions of the muscle fibers in the 

 walls of the oviducts, which move them along by a "milking" 



{ 47 } 



