1 882.] Zoology. 137 



how the weight of its contents or the action of its muscles can 

 exert any considerable influence upon its greater portion in man, 

 the above may be regarded as the principal agencies, for sexual 

 selection is confined to capabilities of an active character, and 

 attributes which are displayed, and would be inoperative upon a 

 hidden part, the function of which is only passive. 



In civilized man, however, at all events in the higher grades of 

 modern civilization, natural selection may be said to exert no in- 

 fluence in this direction, war -is too infrequent and engages too 

 small a portion of mankind, while the forces with which it deals, 

 are of a nature to alter the whole aspect of the case. And while 

 adaptation undoubtedly operates, particularly among the laboring 

 classes, upon other portions of the frame to maintain their rigidity, 

 it is only in rare instances that the skull is called upon to support 

 any greater pressure than that exerted by the head gear. 



It is not to be overlooked in this connection, that among semi- 

 civilized peoples where the facilities for transportation are limited, 

 the head is often made to support considerable weights, and ex- 

 cept where rigid rules of caste prevent the intermarriage of classes, 

 the joint action of adaptation and heredity disseminate the effects 

 of this custom throughout the community. 



There probably never was a time in the history of the world, 

 when the skull was subjected to so little violence, as since the 

 introduction of modern methods of transportation, and when we 

 recall the fact, that it was but a few centuries ago, that the most 

 advanced nations of the present day were barbaric, it is too soon 

 to look for any great change. Yet it is not uncommon to hear 

 of cases of fracture of the skull, which are ascribed to its unusual 

 thinness. May not these be the results of fortuitous cooperations 

 of the agencies mentioned? 



If the force of the position assumed is accepted, the logical 

 delusion is that we are approaching a time when the human 

 cranium will become much thinner, so delicate, in fact, that it will 

 be easily fractured, we may therefore expect a revival of natural 

 selection, and an increase of cases of death from violence to the 

 head.— *Ki?. Cooper. 



Habits of the Fierasfer, a Boarder in the Sea-Cucum- 

 ber.— The Holothurians or sea-cucumbers have been long known 

 b y fishermen to harbor a curious fish, to which Cuvier gave the 

 name Fierasfer. Several species of it are known. The most 

 common in the Mediterranean, the Fierasfer acus, has been re- 

 cently made an object of special study by Professor Emery, at 

 the zoological station at Naples. 



io procure Holothurians tenanted by the fierasfer, it is necess- 

 ary to seek the animals at a certain depth ; those living near the 

 shore do not usually contain them. * The two Mediterranean 

 species of holothurians. which are most frequently tenanted, are 

 ^tickopus regalis and Holothuria tuhdosa. When these animals 



