INTEREST OF EMBRYOLOGY. 181 



fish in its progress might occupy one's whole 

 life without being exhausted, so wonderful, 

 mysterious, and complicated are the changes 

 which take place in the course of the organic 

 development. Even to the superficial observer 

 the phenomena cannot fail of being interesting, 

 such as the heart in its action, the cir- 

 culation of the blood in its vessels, the change 

 of form of the blood corpuscles from circular 

 as is their outline in the embryo, to elliptical, 

 as they are in the fully formed young fish, 

 such, moreover, as the advanced state of some 

 of the organs at an early period, the eyes and 

 pectoral fins, for example, and the late pro- 

 duction of others, the dorsal and abdominal fins, 

 for instance, the scales, its defensive armour, 

 which are but slowly formed, no traces of them 

 existing in the fcetal fish. Even, in what is 

 abnormal, there is an interest ; as in animals 

 of higher organisation, so in these, occa- 

 sionally marks of imperfect or partially ar- 

 rested development may be witnessed; thus, 

 I have seen a young salmon, destitute en- 

 tirely of eyes, otherwise on quitting the egg 

 well formed, and at the same time active, and 



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