GREA T BRITAIN. 35 



its allies filaments pass from all sides of the eggs, and thus 

 attach them to any passing or stationary object. 



But there are other marine forms termed anadromous, 

 which leave the ocean, migrating into rivers, up which they 

 ascend, often for long distances, and where they deposit 

 their eggs, as the shad, salmon, or lampreys. Although 

 the freshwater forms are not included in this Paper, I may 

 remark that there are certain families of them in the tropics 

 in which they are strictly monogamous, building nests, as 

 a rule, for the reception of their eggs, and guarding their 

 young until able to shift for themselves. 



Our sticklebacks, both marine and fresh-water, construct 

 nests for the reception of their eggs, the fifteen-spined one 

 usually selecting a sheltered spot which pure sea-water 

 reaches. Here it collects some of the softer kinds of green 

 or red seaweed, which it joins with coralline tufts and 

 threads, forming a pear-shaped structure, about as stout as 

 a man's fist. Some tropical siluroids which do not form 

 nests have a peculiar mode of protecting their eggs, the 

 male carrying them about in his mouth. 



Considering how the eggs of fish are deposited in the 

 sea, it does not seem wonderful should many escape fecun- 

 dation, and this would be probably still more common in 

 such as are deposited in rivers. It is well known that eggs 

 are a tempting bait for this class of animals, while they 

 likewise are generally partial to fry, even of their own 

 kind. In fact, we perceive some forms, as the sticklebacks, 

 in which the male will guard the nest and protect the eggs 

 and young, but after they attain to certain size, should 

 they not depart and shift for themselves, the probabilities 

 are that they will be devoured by their progenitors. Next 

 we have forms, such as the salmons, that make a red or 

 nest in the gravel at the bottom of a river, and subse- 



D 2 



