THE HERRING FAMILY. 425 



Raffaele, working at Naples, found a particular pelagic egg 

 in the tow-nets which he considered to be that of the pilchard. 

 This egg presents many striking features (Plate IV, fig. 23). 

 It has a large perivitelline space between the egg itself and its 

 outer membrane, a characteristic which is found in such an 

 entirely different species as the long-rough dab, but it may 

 be at once distinguished from the latter by the presence of an 

 oil-globule which is in the usual position, within the yolk-sac. 

 Raffaele gives the diameter, over all, as 1*5 to 1'7 mm., that of 

 the egg proper as '8 to '9 mm., and that of the oil-globule as 

 16 mm. The yolk is covered with large reticulate markings, 

 due to the mass being composed of radial sections which are 

 compressed tightly together, leaving polygonal surface-markings. 

 This feature is well developed in the sprat's egg, and an allied 

 form of yolk-structure is found in that of the herring. 



The herring, the sprat and the pilchard are about as closely 

 allied species as are to be found, yet the eggs of the three could 

 not possibly be mistaken, for in the first case we find a small 

 opaque demersal egg occurring in masses, in the other two a 

 translucent floating egg, both with polygonal yolk-markings, 

 but the latter having a large perivitelline space and an oil- 

 globule. This great diversity in the structure of the egg is 

 found to extend still further in the case of the egg of the 

 anchovy, which Raffaele describes from Naples and one of us 

 from Lytham, and which is almost unique amongst pelagic 

 types in being of an elongated form. It is not uncommon to 

 find a departure from the geometrical accuracy of a sphere in 

 some species, but the anchovy's egg may be almost described 

 as cylindrical in outline. (See Anchovy.) 



Raffaele succeeded in hatching the eggs above referred to, 

 and found that the period of incubation lasted from four to five 

 days. The temperature of the tank-water during this time 

 varied from 9 C. to 12C. He also gives a view of the egg 

 with its contained embryo at a fairly advanced stage of de- 

 velopment. 



Cunningham has since found eggs corresponding to Raffaele's 

 description in the tow-nets at Plymouth, and agrees with the 

 latter in regarding them as those of the pilchard. There is 



