534 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVIII. 



Since the egg tube is secreted only as there is a demand for more 

 space and is extended by the pressure of the issuing eggs, it follows 

 that this pressure, acting always along the axis of the egg tube, flattens 

 the egg at right angles to that axis. Each egg assumes a biscuit shape, 

 with the exception of the one first extruded, which is hemispherical. 

 The form is usually fairly symmetrical, the pressure being equally 

 distributed, but sometimes an egg will get flattened on one side more 

 than the other (see fig. 2). 



The germinal area is about in the center of the proximal side of the 

 biscuit in the great majority of cases. But here again there are excep- 

 tions and occasionally an egg is reversed as 

 it issues and the germinal area appears at 

 the center of the distal side. From this 

 center the embryo spreads gradually until it 

 covers the flattened side and extends down 

 over the edge of the biscuit, so that in 

 advanced development the appendages can 

 be distinctly seen on the edges of the eggs 

 under a high power (see fig. 35). Not only 

 are the germinal areas thus all upon the 

 center of the proximal sides of the eggs, 

 but the S3 7 mmeti\v is carried still farther in 

 the fact that the longitudinal axes of the 

 embryos are very closely parallel. This 

 brings the corresponding appendages of 

 the different embryos in longitudinal rows 

 along the sides of the egg tubes. 



The eggs also change in color with ad- 

 vancing development. At first colorless or 

 with a yellowish tint, they gradually assume 

 the color of the pigment which is to distin- 

 guish the nauplius when it finally becomes 

 free. 



This color varies in different species and 

 is readily visible to the naked eye against 

 a white background for some time previous to hatching. If the living 

 copepod be placed in a porcelain dish and examined with a hand lens 

 the color shows to good advantage. It is so constant in the same 

 species and so distinct in many of them as to afford a good supple- 

 mentary evidence of identit}" in females carrying f ulty developed eggs. 

 There is no regular breeding season. Females with f ully developed 

 eggs are found alongside those with egg strings only partially extruded 

 or with none at all. And oftentimes a single fish will } T ield these 

 different adult forms and several chalimus stages. But while there is 

 this great irregularity in the breeding season of different individuals, 



Fig. 35. — Portion* of an egg-string 

 op Caligus bonito. (Highly 

 magnified.) 



