26o UNIVERSITY OF COLORADO STUDIES 



motion they created on trying to get to deeper water. All along the 

 shore the few individual ones — which before had been found very 

 close to rocks and grasses — began now as the Spirogyra advanced all 

 along these two borders to be more closely connected with the green 

 masses than with the rocks. The shoal was made up of larval forms 

 in all stages of development. Some were in the full larval condition 

 with long gills and thick (dorso-ventrally) tail; in some the tail was 

 partially absorbed; in others the gills. In some few both of these 

 changes were taking place. Where absorption of the gills was occur- 

 ring, it seemed to be more in the third one than in the two more 

 forward. 



The southwest corner of the lake was a very shallow place with 

 a muddy bottom. With exception of the inlet this was the only 

 place on the lake which had been covered with Spirogyra. This 

 place was examined daily from June i6, and although numerous 

 larvae were taken from it, no adults were seen until June 24. There 

 were only six of these, and as they were shown to be pure adults by 

 the development of the genital organs and distribution of the aortic 

 arches, and as no intermediate stages were found at the time, it is 

 probable that they were last year's adults. These when disturbed 

 were just as likely to swim toward the shore as toward deep water. 

 They would allow themselves to be caught in a net without any par- 

 ticular struggle. On land they were very much more at home than 

 were the larvae. When in motion they used the tail very little. They 

 seemed to prefer to crawl along the bottom with their feet; when 

 swimming they used their feet mainly, i.e., they would give a big 

 shove with them, then they would lay them alongside of the body and 

 would gUde through the water until the motion was spent, after which 

 they would repeat the act. 



All this time the larvae had been breathing entirely by means of 

 gills and skin, but on June 25, 1909, I noticed that a larva after 

 being under water for about two minutes would come to the surface, 

 take a gasp of air and then go down for another short period, after 

 which it would come for another gasp of air. This signified that 

 the lungs were beginning to function. At this time the limbs seemed 



