COURTSHIP AND NURSERY DUTIES. Ill 



of the insect. By this means the female is 

 enabled to deposit her eggs within the open 

 valves of fresh-water mussels, and thus the eggs 

 are placed out of the reach of enemies. 



We may now turn our attention to that vast 

 majority of fishes which neither build nests nor, 

 in the majority of cases, show any sustained 

 regard for their progeny, save only a certain 

 caution in the selection of the site for the deposi- 

 tion of the eggs, which suggests but little more 

 than a kind of obedience to custom. That there 

 is something more than this at work we must, 

 however, feel convinced when we come to review 

 the facts which have been gathered together on 

 this subject. There seems to be ample proof 

 that the parental instinct is by no means slug- 

 gish, and that the deposition of the eggs is often 

 only accomplished after the severest obstacles 

 have been surmounted. 



The eggs of the lamprey, which we distinguish 

 by the scientific name of Petromyzon marinus, are 

 very tiny, and enclosed in jelly-like membranes. 

 But the eggs of the allied forms, Bdellostoma and 

 Myxine, are quite different. In the first place, 

 they are very large and cocoon-shaped structures. 

 Furthermore, they are remarkable for the fact 

 that at each end of the egg there is a bundle of 

 thread-like processes terminating in little hooks. 

 These hooks are for the purpose of interlocking 

 with the corresponding processes of other eggs, 

 and with sea-weed at the bottom of the sea. 



The eggs of the sharks, and rays or slcates, 

 must be familiar to all, since those of the skate, 

 at least, are commonly to be seen strewn along 



