1874.] 171 [Garman. 



upper teeth, effectually prevents the water filling the interior from 

 passing out through the mouth-opening when feeding, and the struc- 

 ture of the gill-openings prevents an inward flow through them, so 

 that but one course is open for the current. 



Passing to the skates we find the spiracle deprived of the reflexed 

 valve, but in other respects it exists as before ; here the water may- 

 pass either way. The principal use of the cartilage and muscle is 

 to close the aperture at the will of the animal, as on occasion of the 

 head being thrust into sand. Further along, among the flattened 

 Selachians, as long as their main dependence is on the sense of smell 

 in seeking food — the olfactories retaining their great development, as 

 compared with the eyes — so long the spiracles are well developed ; 

 but as soon as we approach creatures more dependent on the eyes, 

 as the sharks, the spiracle begins to disappear, until amongst those 

 having nictitating membranes, whose eyes have comparatively great 

 freedom of movement, and who are no longer dependent on the nose, 

 it is found to be nearly or quite obsolete, as in Carcharias and 

 Zygcena. 



The development of the spiracle is in direct proportion to the 

 development of the organs of smell, and in inverse proportion to that 

 of the organs of sight. 



The credit of the discovery of the functions of the claspers is due to 

 Professor Louis Agassiz. At the meeting of the American Academy, 

 held in Cambridge, during the winter of 1872-73, he showed conclu- 

 sively, by means of dissections and drawings, that they were intro- 

 mittent organs. His preparations were made some years previous, 

 but he had not before, to my knowledge, published the facts. The 

 dissections exhibited before the Academy were made to show the 

 muscles by which the claspers were erected, turned and carried for- 

 ward, their ends expanded and turned outward, and the manner in 

 which the grooves on their sides were brought over the openings of 

 the spermatic ducts so as to lead the fluid into the oviducts of the 

 female. 



As the Professor remarked at the time, Aristotle's comparison of 

 the sharks with dogs, as to the manner of copulation, is well sup- 

 ported by the facts. During the past summer it was with great 

 pleasure that I observed a fact that adds a little emphasis to his dis- 

 covery. The hint which led to the establishment of the fact that the 

 virgin females of the sharks have the oviduct closed by a membrane, 

 that they possess a hymen corresponding to that of the mammals, was 



