1894 THE MICROSCOPE. 71 



as right and left spermaries. A duct leads from tlie 

 spermaries to the anus. The ovaries of the female are 

 placed in the same relative jDosition, and are known as 

 the right and left ovaries. The color of the ovaries is 

 yellow, while that of the spermaries is white. 



The eggs are found in the ovary in different stages of 

 developement. Some almost fully developed and others 

 in the first stages are totally undeveloped (Fig. 3). 



The ova are all enclosed in a fine porous membrane — 

 the vitelline membrane. Among the ova may be seen 

 many minute drops of oil. By placing the ova in ether 

 for a few hour^ the oil is completely extracted. The 

 undeveloped ovum contains simply the nucleus and proto- 

 plasm. In the developed ova the protoplasm has formed 

 a net work throughout the ova, and the interstices are 

 filled with yolk. 



10. The back-bcne extends from the head to the root 

 of the caudal fin (Fig. 2). It is made up of a number 

 of vertebra. Each vertebra bears two or more spines, 

 according to its position. The vertebra itself is called 

 the centrum, and is, in cross section, almost square. 

 The centrum is slightly longer than it is broad. The 

 ends of the centra are concave and a canal runs longi- 

 tudinally through the centra. This canal contains the 

 noto cord, a cartilaginous body, which swells out at the 

 junction of two centra and fills the space caused by the 

 concavity of the ends. 



From the top of each vertebra rises a spine, (the 

 neural spine.) To form this spine it seems as if a spine 

 had grown upward from each side of the centrum, and 

 after a time had joined, forming a canal at the base of 

 the spine, through which runs the spinal cord. Until 

 the body cavity is passed the centrum bears a curved 

 spine or rib on each side. Back of the body cavity there 

 are no ribs, but the centrum bears a ventral spine, shaped 

 as the neural spines, and through the haemal arch runs 



