CHAPTER THIRD. 



EMBEYOLOGICAL CLASSIFICATION OF STAEFISHES. 



The study of the young forms, or morphological embryology, if I may so call it, is 

 destined to play an important part in Systematic Zoology ; though investigations of 

 this kind can only be carried on under peculiar advantages not easily obtained. The 

 fact that many marine animals live, in their early stages, under stones, or firmly 

 attached to roots of Laminarians, in deep water, and are only occasionally thrown 

 upon the beaches after storms, when their small size prevents us from obtaining 

 them in any great number, increases the difficulty of this kind of observations. 

 "We must, therefore, limit ourselves to those animals which pass the greater part of 

 their lives near the surface of the water, or within the limits of tide-marks. A 

 commencement has already been made in this direction, in the study of Fishes, the 

 young of which live among the eel-grass, and of the young of the several species 

 of Ctenophorae, which are so abundant during the summer months along our coasts. 

 For an account of these investigations, I would refer the reader to the Illustrated 

 Catalogue of the Museum of Comparative Zoology. 



Comparison of young and adutt Starfishes. — The difference in appearance between 

 the young and the adult of our Starfishes is so great, that they would not be 

 placed in the same family by one unacquainted with their transformations. The 

 young has characters which, if taken singly, recall a variety of families ; in fact, 

 the combination of characters belonging to different families is almost always a sign 

 that these features will disappear, or become modified with age. 



Here I must again insist on the importance of the constant comparison of the 

 younger stages of growth with the adult. We are so little accustomed to consider 

 these younger stages in our description of animals, that we necessarily lose many 

 elements of the greatest importance, whenever we attempt to associate the adults 

 of any class in natural groups, without taking into account the characters of 

 their young; and naturalists, who have not yet entered upon this method of study, 

 cannot conceive what extraordinary facilities this kind of investigation affords for 

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