FORMATION OF PROTECTIVE EMBRYONIC MEMBRANES 907 



ooporphyrin pigments, derived probably from the hemoglobin of worn-out 

 red blood cells. A thin cuticle or protective film is applied to the surface of 

 the calcified spongy layer just before the egg is laid (fig. 369B). 



The rate of transport of the egg through the oviduct of the hen is inter- 

 esting. Once the egg has entered the infundlbulum, it takes but 20 minutes 

 to complete its passage through this area. The infundibular region constitutes 

 five per cent of the length of the oviduct. In the albumen-secreting region 

 where it accumulates most of its albumen, the egg spends about four hours. 

 This segment forms about 60 per cent of the total oviducal length. The passage 

 through the isthmus requires approximately one hour. This region forms 15 

 per cent of the total length of the oviduct. The last or uterine segment is 

 about the same length as that of the isthmus, but the egg spends about 80 

 per cent of its passage time or about 19 hours in this portion. The rate of 

 passage, therefore, in the more anterior portion of the oviduct is rapid, some- 

 what slower in the isthmus, and very slow in the uterus (Romanoff and 

 Romanoff, '49). 



3) Reptiles. Egg passage through the oviduct and deposition of the tertiary 

 egg membranes in reptiles probably resembles very closely that of the bird with 

 the exception that in a considerable number of reptiles the young develop in 

 the uterus and are discharged in a free-living condition (see p. 83 ). Also, the 

 eggs of modern reptiles have a thick leathery shell instead of the brittle cal- 

 careous shell of bird's eggs. 



4) Amphibians. In the frog, egg transport down the glandular portion of 

 the oviduct appears to be effected mainly by the propelling force of the 

 beating cilia, possessed by certain of the cells lining the oviduct. This ciliary 

 action possibly is aided by some peristaltic action of the oviducal musculature. 

 The cilia are found on the cells which line the longitudinal ridges which run 

 "more or less the length of the oviduct" (Noble, '31, p. 282). As the egg 

 moves downward (posteriad), it is covered by mucus or similar gelatinous ma- 

 terial. In the common frog, Rana pipiens, three gelatinous layers are deposited 

 around the egg during its oviducal passage. 



Passage of the egg through the oviduct in other Amphibia probably resem- 

 bles that of the frog. 



In many Amphibia (e.g., frogs), the caudal portion of the oviduct is ex- 

 panded to form a special compartment, called the uterus, where the eggs 

 remain for a period before discharge to the outside. In some urodeles, the 

 eggs are retained in the oviduct, and the young are born in the larval or 

 fully metamorphosed state (see p. 189). 



5) Fishes. Internal egg transport in fishes presents a variety of conditions. 

 In many teleosts, the ovary, when egg formation is completed, becomes a large 

 egg sac, directly connected with the short oviduct. At the time of spawning, 

 a general contraction of the ovarian tissues occurs, and the eggs are expelled 

 into the oviduct and from there to the outside. The contraction of the ovarian 



