Instincts, Habits, and Adaptations 173 



we have in these fishes a mouth gestation. In the mass of 

 eggs with which the mouth is filled I have occasionally found 

 the eggs, rarely more than one or two, of another species. The 

 only way in which their presence may be accounted for, it 

 seems to me, is by the supposition that while feeding the eggs 

 are disgorged, and as these fishes are gregarious in their habits, 

 when the ova are recovered the stray eggs of another species 

 may be introduced into the mouth among those which natu- 

 rally belong there." 



One of the earliest accounts of this curious habit which 

 we have seen is that by Dr. Giinther, referring to specimens 

 of Tachysurus fissus from Cayenne received from Prof. R. 

 Owen: 



"These specimens having had the cavity of the mouth and 

 of the gills extended in an extraordinary manner, I was induced 

 to examine the cause of it, when, to my great surprise, I found 

 them filled with about twenty eggs, rather larger than an ordi- 

 nary pea, perfectly uninjured, and with the embryos in a for- 

 ward state of development. The specimens are males, from 

 6 to 7 inches long, and in each the stomach was almost empty. 



"Although the eggs might have been put into the mouth 

 of the fish by their captor, this does not appear probable. On 

 the other hand, it is a well-known fact that the American Silu- 

 roids take care of their progeny in various ways; and I have 

 no doubt that in this species and in its allies the males carry 

 the eggs in their mouths, depositing them in places of safety 

 and removing them when they fear the approach of danger or 

 disturbance." 



The Unsymmetrical Eyes of Flounders. In the two great 

 families of flounders and soles the head is unsymmetrically 

 formed, the cranium being twisted and both eyes placed on the 

 same side. The body is strongly compressed, and the side pos- 

 sessing the eyes is uppermost in all the actions of the fish. 

 This upper side, whether right or left, is colored, while the eye- 

 less side is white or very nearly so. 



It is well known that in the very young flounder the body 

 rests upright in the water. After a little there is a tendency to 

 turn to one side and the lower eye begins its migration to the 

 other side, the interorbital bones or part of them moving before 



