LIMITATION IN LOWER VERTEBRATES 135 



submerged or demersal eggs. These are larger and are heavier than 

 sea-water. Herrings, although they swim near the surface, lay 

 demersal eggs, and a similar habit has been adopted by the wolf- 

 fish, gobies, suckers and many others. A certain amount of choice 

 is shown in the selection of the ground for depositing the eggs, and 

 these are usually enclosed in a firm and sticky capsule, or embedded 

 in lumps of mucus which enables them to adhere to seaweed or 

 stones. The numbers are much smaller, and are to be counted in 

 thousands, hundreds or dozens. The herring, which is the most 

 prolific of these fish with demersal eggs, deposits about twenty 

 thousand. Fishes, like salmon, which ascend rivers from the sea, 

 and most of the fresh-water fish, are also demersal, and many 

 of them show a certain amount of care in the deposition 

 of the eggs, scooping out holes and covering them with sand or 

 stones. 



There is a heavy toll taken of unprotected demersal eggs, and 

 there are many remarkable instances in which brood-care goes 

 much beyond the mere choice of a locality for laying the eggs. The 

 spawn is often sedulously guarded by one of the parents, and it is 

 interesting that this duty is almost invariably assumed by the male. 

 The common British butter-fish (Pholis gunnellus) coils its body 

 round the mass of eggs, the male and female relieving one another 

 in this task, and then, after a time, hiding them in holes scooped in 

 the rocks by some of the boring molluscs. The female lump-sucker 

 attaches her eggs in sticky masses to rocks or logs and then takes 

 no further interest in them, but the male watches over them until 

 they hatch out, when the fry cling to his body by their suckers. 

 The sand-goby lays her eggs under the empty shell of a shellfish, 

 such as the scallop, and then the male watches over them until they 

 hatch. J. S. Budgett, who went to the Gambia to study the strange 

 African lung -fish, Protopterus, found that the eggs were laid in 

 circular nests hollowed in the mud on the edges of swamps. The 

 nest was an irregular hole about a foot deep, filled with water, but 

 unlined. It was surrounded by reeds, and these were crushed down 

 at one side, there being a sort of path by which the parent could 

 pass out and in across the little stretch of dried mud separating 

 the nest from the swamp. The female apparently deserted the 

 nest after laying the eggs, but the male stayed on, and was usually 

 found lashing his tail and keeping the water in violent commotion, 

 so that it was better aerated. The male guarded the young larvae 

 savagely, biting at any one who tried to touch them. The young 



