50 Papers from the Department of Marine Biology. 



"The very young fry were also taken into the mouths of the parents and 

 blown out; especially those which became separated from the main lot and 

 were found in sand and sediment. The old fish would take a mouthful of 

 fry and foreign particles, retain them for a moment, and expel them with some 

 force. After the young began to swim and became scattered, the parents 

 continued to suck them in, and, as subsequently developed, did not always 

 blow them out .... 



"The fry which were left with their parents continued healthy, but their 

 number steadily decreased. There being no way for them to escape; . . . 

 it was suspected that the old fish were eating their young .... They were 

 kept under close observation during the day, and were seen to be fond of mouth- 

 ing the fry, more especially the weaker ones .... They were frequently 

 seen to follow leisurely a fry, suck it into their mouth, retain it for a while, 

 and then expel it, sometimes only to capture it again. There was no active 

 pursuit of the fry, and the tendency seemed to be to spit them out. In one 

 or two instances, however, it appeared that fry taken into the mouth were 

 not liberated, the feeding instinct becoming paramount to the paternal in- 

 stinct. After all the fry which had been left with their parents had disappeared, 

 in about 6 weeks after hatching, 18 fry were placed in the aquarium one even- 

 ing, and only 2 of these survived on the following morning. " 



It seems hardly necessary to argue the question as to the origin of 

 the habit of oral gestation after the presentation of the facts above 

 given. In the mind of the present writer there is no doubt that 

 having begun by taking up the eggs and young for purposes of trans- 

 portation, the fish have presently learned to retain them for longer 

 and longer periods of time; we have a record of at least one minute's 

 retention; and as the fish which retain their young even for short 

 spaces of time and transport them to safer localities are more likely 

 to leave descendants, through the action of natural selection, these 

 fish and this habit will be perpetuated. Hence we may conjecture 

 that as tune has gone on the habit of retention has become more and 

 more fixed until finally oral gestation has become an established habit. 



Nor does the matter of abstinence from food offer any difficulty 

 just here. It is known that many fishes which guard their nests do 

 not feed while on such duty, and this is particularly true of the stickle- 

 backs and gouramies. So this fits in well with the conjectural expla- 

 nation just offered. 



To the present writer all the data available lead to the conclusion 

 just set forth, and to it he gives his full adherence. 



