2OO CARL L. HUBBS. 



California, and that there is some variation in the time of their 

 formation. 



METAMORPHIC ANNULUS. 



The scales of even the largest embryos of Auiphigonopterus 

 aurora and of Micrometrus miniums are marked from focus to 

 border by evenly spaced, concentric striae ; those of all but the 

 most recently born young, on the other hand, are marked near the 

 margin by a zone in which the circuli are finer and more closely 

 approximated than on either side, and frequently angulated, their 

 course on the scale within this zone being slightly different from 

 that without. This mark, which is formed during the summer, 

 resembles the winter checks or annuli formed farther out on the 

 scales of older fishes, and perhaps quite as closely simulates the 

 annulus on the scales of the Pacific salmon. As a distinctive 

 name, the term metamorphic annul us is proposed for this mark. 

 It is likewise indicated on the scales of Cymatogaster aggregatus 

 and of other species of the family ; the time of its formation (as 

 indicated above soon after birth during the summer) has been 

 confirmed in the case of Embiotoca lateralis. 



The cause leading to the formation of the natal annulus is ap- 

 parently a temporary retarding of growth immediately after 

 birth, just as the other annuli are supposed to be formed as a 

 consequence of the decreased nutrition and growth of the fish 

 during the cold season. In this connection there should be re- 

 called the sudden alteration of the method of feeding and respira- 

 tion forced upon the young of these fishes at birth. They are 

 then cast out into a very different medium, from which oxygen 

 must be absorbed mostly through the gills, rather than through 

 the skin and the tips of the fins. Instead of merely passing 

 through themselves the nutritive fluid with which they were sur- 

 rounded, they must now feed in the normal fashion of fishes. It 

 is obviously these changes in the manner of living, which stamp a 

 lasting mark on the scale. The metamorphic annulus significantly 

 is usually more sharply evident in the males than in the females 

 of those embiotocids known to be characterized by the natal ma- 

 turity of the males. 



