EGG-PURSES OF RATS, ETC. 341 



flows while the young fish is being matured, and 

 by which it eventually issues forth from its very 

 singular envelope. 



Kemarkable, however, as these " sea-purses " are 

 in form and structure, there is one particular re- 

 garding them which presents us with a most 

 striking instance of a provision made for the wants 

 of the young fish before it is able to quit its 

 prison. During its embryo state it cannot use its 

 gills for the purpose of breathing, any more than 

 an infant before birth can employ its lungs in 

 breathing. Yet in order to the development of the 

 fish, it is indispensable that through its circulating 

 system the blood shall pass purified by the action 

 of the water, and supplied with oxygen as it is re- 

 quired. Without this process the young fish must 

 perish. And how is this accomplished ? By a 

 very marvellous expedient. From the gills of the 

 young fish project certain threads or filaments ; 

 each of these contains a minute blood-vessel, and 

 as the water has free ingress to the interior of the 

 receptacle, these blood-vessels serve the purpose 

 of gills. They are, however, entirely temporary ; 

 they^cease to exist after the gills are capable of 

 acting. The purpose they had to serve is accom- 

 plished otherwise, and by an apparatus possessed 

 of a degree of efficiency suited to the enlarged 

 powers of the fish. Can any mode be devised by 

 which to account for the admirable appropriate- 

 ness of this structure, but that of referring it to 

 the wisdom and skill of the Creator ? The supply 

 of a temporary breathing apparatus to be used 

 z 3 



