THE GROWTH AND REGENERATION OF THE 

 GILLS IN THE YOUNG NECTURUS. 



ALBERT C. EYCLESHYMER, 



DEPARTMENT OF ANATOMY, ST. Louis UNIVERSITY, ST. Louis, Mo. 



During the summer of 1904 the writer made a series of obser- 

 vations and experiments on the growth and regeneration of the 

 gills of the larval Necturus. The work was done with the hope 

 of obtaining more information as to the relation which the regen- 

 erated gill bears to the normal in its rate of growth, in its size, 

 and particularly in its pattern. 



The larvae were kept in aquaria, from which they were taken at 

 intervals, placed in flat-bottomed watch-glasses above mirrors, 

 and sketches made of the ventral surfaces of the gills. The 

 period of observation on the growth of the normal gills was 

 from the time (1213 nim) of their first appearance, to the time 

 (18-20 mm.) when four pairs of filaments were present. At this 

 time the gills were cut off and preserved. 



These larvae were then placed in separate aquaria and like the 

 normal were sketched at successive intervals. The period of ob- 

 servation on the regenerating gills was from the time of excision 

 until about the same number of filaments were present as in the 

 normal at the time when they were cut off. 



Ten series were started, but only eight were completed, owing 

 to the death of two larvae. That the normal processes might be 

 as little disturbed as possible but a single gill was removed from 

 each larva. This one was in each case the anterior on the right 

 side of the head. Since the eight experiments gave similar re- 

 sults, but three have been described and illustrated in detail. 



The first appearance of the gill bars is to be seen in the 9-10 

 mm. larva as slight swellings on each of the three gill arches. 

 When the larva has reached a length of 12-13 mm., the first and 

 second gill bars measure about i.o mm., while the third measures 

 0.5 mm. 



The first gill filament appears at this time as a slight swelling 



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