NIDAMENTAL TISSUES 487 



(outer) ends. In transverse sections of the oviduct these tubular glands 

 have been mistaken for sections at right angles to longitudinal corruga- 

 tions. The right-hand part of our figure, although a transverse section, 

 gives proof that such is not the case in this form, and that the folds 

 in the section represent glands of a tubular variety. 



The cells lining these glands form a columnar epithelium, and are 

 intensely active in secreting the jelly substance. The secretion appears 

 as a granular mass that fills their distal ends. The nuclei lie flattened 

 against the proximal surface, and are very small and dense. The outer 

 edges of the folds represent the primary surface of the duct lumen. 

 Here the gland cells give way to a non-secreting form with a larger 

 nucleus placed in the middle height of he cell. 



The whole tube is surrounded by an inner and an outer longitudinal 

 layer of smooth muscle. The ovum is passed through the tube by a 

 wave-like contraction of these layers, which is called peristalsis. 



The fish, Pterophryne histrio, is one of a large group, the pediculate 

 fishes, which lay their eggs embedded in a long ribbon-shaped plate of 

 jelly which floats on the sea until the eggs hatch. 



This ribbon of jelly is made, not in an oviduct, for the bony fishes 

 have no long oviduct, but by a part of the ovary itself. This organ, like 

 that of other teleosts, is a tube-like sac formed by the union of two epithe- 

 lial folds. In a mackerel and in most other members of this group the 

 entire inner surface of this long pocket is used to produce the ova. In 

 Pterophryne the sac hangs from its suspensory membrane, with its lumen 

 closed to a straight line and its cylindrical wall thereby divided into two 

 halves which rest against each other, face to face. One side is used to 

 develop the ova, and this side is raised into the numerous evaginated pa- 

 pillae that occur in the other teleost ovaries. The other and opposite side 

 retains its simple epithelial structure, and the epithelium secretes the 

 jelly materials in the form of a flat sheet, the exact length and width of 

 the layer from which it originated. The jelly strip and the ova are pro- 

 duced at the same time, and then* position, opposite and against each 

 other, causes the ova to be pressed into the jelly, and then the whole 

 mass is passed out of the ovary, one from each of the two divisions, and 

 the jelly swells a little and floats about until the eggs develop. Figure 

 457 represents a fold (not a gland) of this membrane in section. The 

 skate, Raja erinacea, will serve to represent the third vertebrate type to 

 be described, in which the ovum is covered first with a coat of jelly-like 

 albumen, and afterward with a tough shell of rather remarkable shape. 

 As in the amphibian, the ovum is set free from the ovary into the body 

 cavity and is then conducted, probably by ciliary motion, into the opening 

 at the anterior end of the tube-shaped oviduct. This wide opening soon 

 narrows down, and in its upper part the albumen covering is secreted 



