174 PLANKTON OF WISCONSIN LAKES 



of Oligochaeta, but it is about the same as the percentages in most of 

 the copepod material and in some of the insect larvae. 



Insect Larvae. Eight samples of aquatic insect larvae, from Ephe- 

 merida to Corethra plumicornis inclusive in table 49, were analyzed. 

 The specimens of Sialis infumata consisted of larvae that had migrated 

 to the shore for the purpose of pupating ; this material, therefore, rep- 

 resents the full grown larvae. The two samples of Corethra also were 

 full grown larvae ; the other five samples contained insect larvae of 

 different sizes, thus representing different stages in the growth of these 

 forms. 



In these eight samples of insect larvae the nitrogen varied from a 

 minimum of 7.36 per cent in Chironomus tentans to a maximum of 

 10.74 per cent of the dry weight of the material in Corethra punctipen- 

 nis; on an ash free basis the range is from 7.76 per cent to 11.67 per 

 cent of the organic matter in these two forms. The crude protein in 

 these larvae, therefore, made up from 48.5 per cent to 72.94 per cent of 

 the organic matter. The ether extract showed more than a twofold 

 variation in percentage, ranging from a minimum of 8.0 per cent in 

 Chironomus tentans to a maximum of 18.5 per cent of the dry sample 

 in Sialis; on an ash free basis the former becomes 8.43 per cent and 

 the latter 19.44 per cent of the organic matter. The Sialis larvae were 

 provided with reserve food to carry them through the pupating period 

 of two weeks or more and the high percentage of ether extract indicates 

 that part of this reserve probably consisted of fat. 



The percentage of crude fiber or chitin showed a little more than a 

 threefold variation in these samples of insect larvae, with a minimum in 

 Sialis and a maximum in the Anisoptera. The nitrogen free extract 

 reached a minimum in the Zygoptera larvae and a maximum in Chiro- 

 nomus tentans. The latter, in fact, yielded a larger percentage of 

 nitrogen free extract than any other sample of animal material. Small 

 amounts of pentosans were found in three of the samples. 



The ash varied from a minimum of 4.76 per cent in Corethra plumi- 

 cornis to a maximum of 15.11 per cent of the dry weight in the Trichop- 

 tera larvae. Seven of the samples yielded less than one per cent of 

 silica, while the eighth, consisting of Ephemerid larvae, possessed 3.85 

 per cent. 



On an ash free basis the percentages of nitrogen in the samples of 

 insect larvae show about the same range of variation as the various 

 samples of plankton Crustacea; also some of the former are substan- 

 tially the same as the percentages of nitrogen in the other four samples 

 of animal material, namely, the crayfishes, the amphipods, the worms, 

 and the leeches. The leeches yielded a slightly larger percentage of 

 nitrogen than the maximum of the insect larvae. 



