486 



HISTOLOGY 



layer, a soft albuminous layer, two membranous layers, and finally a 

 hard outer shell for each egg. 



The first type of organ mentioned will be well represented by the ovi- 

 duct of the salamander, Desmognathus fusca. The specimen represented 

 in Figure 456 was killed a short time (a few weeks) before the breeding 

 season, and consequently the nidamental tissues were preparing for their 

 task by an increase in the size and characters of their specific cells. 



This tissue consists of a long tube with an expanded open end that 

 lies far forward in the body cavity. From this end it takes a curving 

 course to the point at which it empties into the cloaca. The ova enter its 

 upper end by the action of ciliated cells, and, while on their way down its 

 lumen, each one is' invested by two coats of a jelly substance. These 



FIG. 456. Transaction of an oviduct of the salamander, Desmognathus fusca. X 80. 



coats are not as thick as they would be in a frog or the salamander, 

 Amblystoma. The outer coat is thinner and tougher than the inner. 

 The inner layer is put on the egg in the upper part of the duct, but no 

 structural differences are to be noted between the glands of this part 

 and those of the point at which the tougher coat is applied. Such a 

 difference must exist, but it may be a chemical difference or one not 

 easily noted in the structure of the cells. 



Figure 456 shows a section of the tube near its upper end, or where 

 the first jelly layer is applied. The large lumen of the duct is closed, of 

 course, in this specimen, owing to the fact that it was not distended either 

 naturally or artificially by any fluids. 



Opening into this lumen are a great many wide tubular glands which 

 show a tendency to become larger or even compound at their proximal 



