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and closed in, contrary to the order of things with eggs generally. 

 The materials of the egg-case were detected in the tubules of the 

 gland of this oviduct, and consisted of granules and long slender 

 threads. The case is formed in the central cavity of the gland, 

 and, as it is built up, the formed portions gradually extend into 

 the lower part of the oviduct. The ovulation of skates resembles 

 that of birds rather than of ordinary fishes. In the latter the 

 eggs are all formed simultaneously, and discharged at once or 

 neai'ly so, while in the former, as in birds, one yolk descends in 

 the oviduct at a time, is encased in the covering, and lost before 

 another can go through the same process. 



Prof. Agassiz said that the communication of the President 

 was of importance, as it bore upon several physiological points 

 now under discussion. He had been shown by the President the 

 egg still in the ovary, (where it must have been fecundated,) and 

 the shell below prepared to receive it. In this connection he 

 was reminded of a fact noticed by himself some time since, with 

 reference to those organs upon the side of the skate called claspers, 

 and which are supposed to be used for prehensile purposes. It 

 occurred to him that they might be organs of copulation, and he 

 found that when they were rotated forwards and upwards, an 

 opening in them was brought opposite to the spermatic duct, and 

 he imagined that they could be introduced readily into the female 

 organs, into the oviducts, and reach the glands described, whence 

 the spermatic fluid would pass up. The President's observations 

 rendered this view of the functions of the clasper still more proba- 

 ble. Plagiostomes have a very different method of reproduction 

 from other fishes. Like birds, they produce few, but large eggs, 

 and these are found to be of various sizes and different degrees 

 of development in the ovary, indicating that several years are 

 required for their perfect maturity, as is the case in turtles. 

 These facts and others serve to confirm the affinities of the sharks 

 and skates, and to separate them from fishes proper. Ai'istotle 

 does not speak of Plagiostomes with fishes, but calls them Sela- 

 chians, and Prof. A. follows the ancient naturalist, giving them 

 the same name. If the Selachians constitute a natural class, 

 then some of the data of palasontology may be better understood 

 than they now are. Fishes are generally considered to have 



