108 CALIFORNIA ACADEMY OF SCIENCES. [ 3 d See., 



of nature. Undoubtedly conditions of temperature and 

 food largely influence the time required. 



Although, my observations on the animals in their native 

 haunts are inconclusive on the point, it appears that they 

 may occasionally remain in the larval state for a much longer 

 time than the usual period. This they certainly do in con- 

 finement and under conditions not so widely different from 

 those which surround them in nature as to make it seem 

 improbable that the same thing may sometimes occur natur- 

 ally. At the present moment, June 16, I have three larvae 

 in an aquarium in the laboratory which have come over from 

 last year's crop, and none of them show any signs of meta- 

 morphosis as yet. Two of these eat well and seem to be 

 in a perfectly normal condition. 1 



In the spring of 1888 a friend of mine, Mr. W. Payzant, 

 and myself hatched a large number of embryos in confine- 

 ment. These all died during the summer excepting a single 

 one, and this lived — as a larva — until January 18, i8g2, 

 nearly four years. It was then killed in order to make sure 

 of it for study before it should undergo metamorphosis. 

 The total length of this specimen, measured just before be- 

 ing killed, was 40 mm. Although it had not grown per- 

 ceptibly since it was about one year old, I do not think this 

 was due to lack of food, because its aquarium always con- 

 tained an abundance of both plant and animal life, and in 

 such balance that the surface of the water was constantly 

 covered with a rich growth of Lemna. 



The largest larva at metamorphosis that I have measured, 

 and certainly as large as any which I have seen, had a total 

 length of 60 mm. But the size, viz., 40 mm., of our four- 

 year old specimen, was undoubtedly much nearer the aver- 

 age of those that have come under my observation than was 

 the 60 mm. individual above mentioned. The smallest 

 specimen at metamorphosis mentioned in my notes was 30 



1 October 9, 1896 — One of these specimens underwent metamorphosis early in August, 

 and noi being permitted to leave the water died on August 10. Another died still in the 

 larval state about the middle of September. The third had died some time before with- 

 out metamorphosing. 



