102 J. T. CUNNINGHAM. 



simultaneously but in succession. In the ovary of a gurnard 

 accordingly, at the commencement of the spawning season, ova 

 in all stages of development are found. In figs. 1 to 5 are 

 shoAvn the appearance under a low power in the fresh state, of 

 a number of eggs of the common or grey gurnard (Trigla 

 gurnard us) at successive stages in the development of the 

 yolk. In fig. 1 the protoplasm is transparent, and contains a 

 small number of globules scattered singly. In the next stage 

 a dark zone is seen commencing to form around the nucleus, 

 and in the outer region of the egg are globules similar to those 

 of the previous stage, but smaller and more numerous. The 

 contrast between the two concentric layers or regions is most 

 marked in the next stage, fig. 3, in which around the light 

 central region indicating the position of the germinal vesicle, 

 there is a very opaque layer sharply delineated externally from 

 an outer more transparent layer. In the next stage, fig. 4, the 

 contrast between the two layers has disappeared, and except 

 for a somewhat lighter ill-defined central region, the whole is 

 nearly uniformly opaque. Eggs which are larger than this, 

 begin to grow transparent again, and the appearance they 

 present is shown in fig. 5. It is easy to perceive from exami- 

 nation of this last stage, that the internal globules are oily, the 

 external vitelline. As the egg approaches the ripe condition, 

 both the oil globules and the vitelline globules begin to fuse 

 together. The large oil globules in the interior of the egg, 

 formed by the fusion of the smaller, are seen in fig, 5. The 

 vitelline globules in fusing form a continuous liquid, in which 

 the still unfused globules remain suspended. The opacity 

 of the egg is due to the small size and great abundance of the 

 globules at the earlier stages, and we learn, therefore, that the 

 greater opacity of the inner layer is due to the smaller size and 

 greater refracting power of the fat globules, which are formed 

 close to the germinal vesicle. 



Similar features have been described by Emery in the deve- 

 lopment of the ovum in Fierasfer acus. The mature 

 ovum of this fish resembles that of the gurnard, having a 

 homogeneous transparent yolk, and a single large oil globule. 



