CHAPTER THIRD. 



EMBRYOLOGICAL CLASSIFICATION OF STARFISHES. 



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; 

 thouo-h 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, \mder stones, or firmly attached to roots of Lami- 

 narians, 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 surfece 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 in 

 that of the young of the several species of Ctenophor?e, 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 Adult 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 disap- 

 pear, 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 but little accus- 

 tomed to consider these younger stages in our description of animals, 



* [See also my papers on Young Stages of Annelids, Ann. Lye. Nat. Hist. ; Young Echini, No. 

 VII. 111. Cat. Mus. Comp. Zodl. ; Embryology of Ctenophora;, Mem. Am. Acad. 1874.] 

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