OF THE SHORT SUN-FISH. 397 



From what I have now stated, it is evident that the interest 

 to be attached to this tissue consists in its purely embryonic 

 character. The general appearance of the cells, their nuclei 

 and nucleoli, the uniformity of the tissue in every part of the 

 animal, and its chemical composition, all indicate this cha- 

 racter ; and when taken in connection with the embryonic 

 state of the bony tissue, and the rudimentary condition of the 

 muscular system, forms a very interesting and important cha- 

 racter in the species, and probably in the order of fishes to 

 which the one under consideration belongs. 



In a teleological point of view it is important, as it points 

 to the existence of certain laws which regulate the develop- 

 ment of animal tissues — namely, first, In the organic scries, 

 tissues as well as forms undergo progressive development; 

 secondly, This progressive development of the tissues may he 

 retarded, retaining their early embryonic condition in certain 

 beings in the series; and, thirdly, Tissue is' subordinate to form? 

 A sun-fish, in fact, as well as other fishes of its order, is as 

 highly developed, in so far as regards form, as any in the 

 class ; in certain of its tissues it is still in the condition of an 

 embryo. 



A second peculiarity to which I shall refer, is the form of 

 the caudal fin of the orthagoriscus. The naturalist is familiar 

 with its truncated shape, but the anatomist has not yet ascer- 

 tained the cause of the peculiarity of this part of the skeleton. f 



* For an exposition of this last law of organisation, see Dr. Martin Barry's 

 Memoir on Embryology, 2d scries, Phil. Trans. 1839. 



+ Meckel, Comparative A natulan, French edition, torn. ii. p. 2S5. For a 

 drawing of the tail, which appears to have heen made from a dried skeleton, 

 see Dr. C. A. S. Schultze, " Ueber die ersten Spuren dea Knochensystems, and 

 die Entwickelung dei Wirbelsaule, in den Thieren." — Meckel's Arckivs, 1818. 

 Willenbergb's drawing, which he states was made from a dried skeleton, is 

 incorrect in the mode of junction of the pectoral girdle to the spine, bul more 

 particularly in tbe mal representation of the mode of termination of the spinal 

 column. He lias mistaken the two or three last vertebrae for a fin-ray and 

 interspinous horn . 



