PLANTS IN PONDFISH CULTURE. 



Previous to the identification of this chironomid m the fishponds 

 the inventory of the plants had disclosed the interesting association 

 of the larval stage of this insect with the alga, Mougeotia genuiiexa. 

 The alga was exceedinglv abundant and produced a most remark- 

 able and beautiful formation. This formation, or algal mat, as it 

 may be called, was composed of delicate, hght-green filaments ot 

 gossamer-like threads which were interwoven intricately m the torm 

 oi loose-meshed rolls suspended near the surface of the water, ihe 

 author's attention was attracted by a large number ot elliptically- 

 shaped bags, or cases, lightly held in the meshes of the algal mat. 

 These proved to be the larval cases of the chironomid in question. 

 AYhile foraging for food the larva? move m and out of their cases, 

 retaining their hold, meanwhile, by their caudal hooks In feeding 

 thev draw toward them filaments from the loose meshes ot Mou- 

 o-eotia, or they forage directly from the outer walls of their cases, 

 to which this alga is applied in the construction of the case, renew- 

 ing the filaments as fast as they become depleted, ihe larva? con- 

 tinue to feed upon this alga as long as the supply lasts, which is 

 o-enerallv only until the middle of July, for by that time this species 

 Sf alga," which flourishes during the early part of the season has 

 passed the stage when floating mats are readily formed. There- 

 after it becomes scattered through the partial disintegration or break- 

 incr up of the filaments. It is at this tune that the diaractenstic 

 " knees " or swellings in the cells occur which give to this torm 9! 

 Mougeotia its specific name, geriufexa It is while engaged 111 

 these feeding operations that the larvae fall prey to the bass. 



Several hundred larvse of OrthodcuJms nivorhimlm were examined 

 to determine to what extent other alga^ contributed to their food 

 supply Tlie determination is a simple matter. The larvae are 

 \\Xi\\ crushed under the cover glass by a slow, forward movement 

 of the thumb, a slight pressure being sufficient to push out the con- 

 tents of the digestive tube. The material is teased out under the 

 microscope, and the problem becomes one of identification ot the 

 alese Almost without exception larvic taken from the mats ot 

 Mougeotia showed a forage value of 100 per cent of this alga. I rom 

 larv5 taken at random in pond 3D, from habitats in which other 

 alo-a" were the chief constituents and Mougeotia appeared only as a 

 sinall factor in the heterogeneous assortment, this alga again tormed 

 the bulk of the food. Specimens of O. nivoHundus were hatched in 

 a watch glass to which liad been added a variety of alga? as well as 

 Mougeotia, and it is interesting to note that the young selected the 

 latteJ invariably. It is not surprising, for Mougeotia is one ot the 

 most delicate of the filamentous forms and possesses a brittleness 

 which apparently recommends it to the larvae, for when observed in 

 their feeding operations they were seen to snap off filame^its in one- 

 coll and two-cell lengths with gi'eat rapidity. This preference for 

 Mougeotia was observed in the very earliest stages of larval growth, 

 and ft continued to be shown to pupation. ^ , . , . , 



Later broods of Orthodmlim nivoriundus, of which there appeared 

 to be three during the summer, found their natural forage among 

 other alga? which succeeded Mougeotia geruuflexa. such as iMovgcofm 

 Hph/vrocarpa, Splrogyra rdtida, S. imi jimvla, (Edogonium, llmho- 

 ,V,clgon r^'fUiilatuni, Lyngbya, and various microscopic lorms present 

 in the algal mats. 



