1M2 Xote on LoverCs Article, on " Leskia mirabilis. Gray." 



XIII. — Note on LoverCs Article on ;< Leskia mirabilis. Gray." 



By ALEXANDER AGASSIZ. 

 Read June 7th. 1889. 



LOVEN has recently, in an article on Leskia mirabitis, Gray, in 

 the Proceedings of the Swedish Academy, taken the opportunity 

 to suggest some views on the homologies of certain openings in 

 ( "\ stideans, tending to corroborate the explanation given by 

 Billings, in the Decades of the Canada Geological Survey, of 

 the functions of these apertures. Lutken has in the Geologist 

 given the main points of Loven's arguments, and at the same 

 time, to a certain extent, criticized the explanations there given j 

 his article has been reprinted in the Canadian Naturalist for 

 December, 1868. to which Billings has added some notes and 

 objections to the criticisms of Lutken. 



I do not intend to pass in review the many theories which have 

 been advanced at various times concerning the probable nature 

 of the ovarian openings, and the openings called mouth or anus, 

 or mouth-anus, by various paleontologists, but simply to point 

 out a few features in the anatomy of recent Echinoderms which 

 seem to have escaped paleontologists when discussing these ques- 

 tions. 



In the first place then' is nothing contrary to the homology of 

 living Echinoderma in the fact that one and the same opening 



should perform at the same time the functions of mouth ami 



anus. But the opening which performs this double function is 

 always the mouth ; it is the opening which in the embryo Echi- 

 noderms is the firsl formed ; when there exists an anus in addition 

 to the mouth, the anal opening is always formed later, and then the 

 mouth performs only its proper functions. As to genital open- 

 COVi red by plates, we find nowhere in recent Kchinoderms 

 any openings so constructed; the only structure to which we 

 might homologize such genital openings is the genital slit of 



