THE STICKLEBACK FAMILY. 227 



tenacious thread. How far one would ask, does the pressure 

 upon the bladder and accompanying distress to the system lead 

 the male fish to build its nest, or how far does the latter act as 

 an intelligent being with a definite purpose outside itself? 

 Who shall say ? 



The straw-coloured, somewhat translucent eggs are of course 

 of the demersal type, and are disproportionately large ('085 inch 

 diameter). The capsule hardens slowly but when it does so it 

 binds the eggs into a compact mass — sometimes three inches 

 by two in diameter. ' The capsule is minutely punctured, the 

 pits being in parallel rows,' ' it is hyaline, very dense and resis- 

 tant.' A great number of small oil-globules are found inside 

 the egg, attached to the investment by minute protoplasmic 

 filaments. As in many demersal types the development was 

 slow ; the period of hatching being from twenty-five to forty 

 days in the tanks with a temperature of from 40° F. to 50° F. 



This difference in the rate of development of the eggs in 

 the nest appears to be due to the fact that the outlying ova 

 hatch more rapidly than those near the centre. 



The embryo is peculiarly free from pigment in the early 

 stages, the first appearance of black spots scattered over the 

 dorsum being on the nineteenth day. The eyes, however, show 

 black pigmentation in some degree as early as the fourteenth 

 day. Three days after this the heart may be noticed as active, 

 and a distinct circulation is established by the nineteenth day. 

 We should emphasize the fact that a plexus of blood-vessels 

 covers the surface of the yolk, a feature not uncommon in 

 demersal ova but confined to that type (cf Wolf-fish). By this 

 date the embryo becomes very restless, movements of the tail 

 and body frequently taking place. 



The larvae, upon hatching (Plate VIII, fig. 8), soon acquire 

 a number of bright yellow pigment-spots scattered over the 

 surface of the trunk, and interspersed amongst these are large 

 stellate black spots, most abundant on the back and sides. The 

 larval stickleback thus is adorned with the same two colours as 

 occur very frequently amongst the pelagic gadoids and pleuro- 

 nectids, but the little animal is far more active and able to take 

 care of itself than is the case with its pelagic allies. When first 



15—2 



