EGGS OF ELASMOBRANCHS 



183 



be covered with a thin layer of sand or gravel, --the 

 spavvners always returning to the same nest, --and a sec- 

 ond, third, and more tiers of eggs will be added. When 

 the eggs have finally been deposited, the nest is fortified 

 by a dome-like mass of pebbles and stones, which the lam- 

 preys carefully drag to the spot. The nest is thus marked 

 out as well as protected, and is said to be made of partial 

 use during the following season. The hatching of the 

 eggs takes place within about a fortnight. 



The eggs which Sharks and Rays deposit are usually 

 enclosed in a stout, horn-like capsule ; this is in general of 

 oblong or rectangular outline, its surface smooth or ridged ; 

 the case of the egg of Scy Ilium (Fig. 189), shows thread- 

 like terminal processes, while these in the ray (Fig. 189^) 

 are stout and spine-like. A great variation may exist in 

 the size of the egg and in the character of its envelopes 

 among the different groups of Elasmobranchs. The egg 

 of the Port Jackson shark, Cestmcion (Fig. 190), is of enor- 

 mous size and possesses an extremely thick, spiral-rimmed, 

 pear-shaped capsule ; that of the Greenland shark, Lcemar- 

 gus, is said to be spherical and relatively small, and to be 

 deposited unprotected by capsule. 



The breeding habits of Elasmobranchs are but imper- 

 fectly known. With the exception, perhaps, of Laemargus, 

 the sexes copulate.* The clasping appendages of the male 

 are inserted either singly or together into the cloaca and 

 oviduct of the female, and the eggs appear to be fertilized 

 in the uppermost portion of the oviduct. The egg then 

 becomes surrounded by a glairy albuminous envelope, and 

 thereafter by the secretion of the oviducal gland, which in 

 the lower oviduct hardens into the horny capsule. The 



* The copulation of sharks has been but rarely observed (e.g. by Bolau in 

 Hamburg ; cf. Kef. on p. 241). 



