consistency of the material there „ Those that swam head-on into 

 a chip or stone lay stimned for a time before -nTiggling about 

 again in apparent search of soft bottom material,. TOien this was 

 found they Immedia.tely burrowed into it. 



Larger ammccoetes, disturbed by crie electric shocker and 

 allowed to drift downstream^ s^vam aimlessly ivith the current until 

 sluggish or slack water was reached. Here they dove to the bottom 

 and burrowed into it if its consistency was suitable o Since all 

 of these larvae are quite blind it would seem that the diving and 

 burrowing behaviorisms are primarily reactions to sluggish currents 

 or slack W3.ter. In responding thus, they are automatically guided 

 to optim-om habitats. 



All sizes of larvae burrow into soft bottom materials with 

 great rapidity, Bodj'- motion in burroiidng is a rapid undulation 

 ivith the posterior iiiird of the trunk describing a figure-eight 

 motion. In somewhat compacted bottcmsj such as those of fine 

 sand J the larvae often rest several times before burrowing com- 

 pletely out of sight o 



In the Ocqueoc River, young-of-the-year up to a length of 20 

 millimeters seldom burrowed more than l/2-inch below the sTirface 

 of the bottom. In aquaria^ specimens 31 to Ul millimeters long 

 seldom went more than 1 l/U inches below the surface; the usual 

 range was 3/U to 1 incho Larvae $0 to 90 millimeters in length 

 generally tunnelled 2 to 3 inches into the bottom, the depth in this 

 size group increasing with the size of the larvae,. Larger indivi- 

 duals, 3.00 to 160 millimeters long^ burroived as deep as $ inches. 

 While excavating a silt bank in the Ocqueoc River _, I discovered that 

 some of the largest ammocoetes (130 to 160 mm. ) may retreat to 

 depths of 6 inches where bottom deposits are particularly soft. 



Aquarium obser^rations were made in running "vrnter aquaria in 

 which an optimum bottom type^ a heavy black muck,, had been p.lacedo 

 About 70 ammocoetes of varying sizes were kept in these tanks for 

 one- to four-week periods^ UShen sand was substituted for the 

 muck, the depth to "vriiich all sizes of larvae burrowed was appre- 

 ciably less. If several inches of muck was present over sand, 

 the larger subjects would cease burrowing do\'mward upon reaching 

 the sandy layer and irould turn toward the surface o 



The burrows in which the ammocoetes live are generally quite 

 ill-defined. This is probably due to the unstable nature of the 

 medium in inhich they are made. As a rule, these burrows are 

 crescent- or broadly "U"-3haped (Figure ^ii). 



Pres^'jmably the lai^rae must ?.ome to the surface of the bottom 

 in crdsT- to feedo In the stomachs of young Entosphenus . Crea.'^er 

 and Hann (1929) found aquatic micro-organisms -which are especially 

 abundant in the thin surface layer of debris on the bottom. Such 

 organisms are not present below this layer. "When ready to feed, 



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