electrical ciorrent evidently cause ruptures of the many capil- 

 laries ■which lie very near the surface in that area. Among 

 shocked specimens subsequently held in aquaria, all evidences of 

 this hemorrhaging disappeared ■^rithin a "week. 



Success in collecting •with the electric shocker depends on 

 being able to see the larvae in the water or on the bottom vrfien 

 they have left their burrows. Turbid water, poor lighting, and 

 the more rapid recovery of the smallest individuals from the 

 effects of the electric current may result in many of these being 

 overlooked. Good random samples of all size groups could only 

 be obtained bj^ exercising greatest care and by working in areas 

 of shallow, clear vrater. 



Some collections -were made by screening dredged bottom sam- 

 ples. I used a Peterson dredge most often and sifted the contents 

 in a box having a bottom of fine-mesh screen. Elcman or other 

 light dredges were unsuitable because the organic debris of the 

 river silt beds frequently prevented the jaws from closing. Scoop- 

 shaped dredges, although satisfactory for collecting, could not 

 be used vihere measures of larval populations per xinit of area 

 were sought. 



The Peterson dredge was selective for the smaller size groups 

 of larval lampreys. It brought up only the surface layer of the 

 stream bottom from about 2 to 2.5 inches in thickness. Such col- 

 lections vfere composed almost entirely of young-of-the-year; 

 sometimes a few yearlings were included. For this reason, they 

 complement those made Tvith the electric shocker since with the 

 latter instrument, the smallest lampreys were most often missed. 

 Both collecting techniques were utilized in seeking total popula- 

 tions of sample larval beds. 



All measurements of the larger aramocoetes were made to the 

 nearest half -millimeter in a small steel trough in which a steel 

 ruler had been mounted. Similar measurements of smaller speci- 

 mens were made on a Bogusch Measuring Slide. Recently-hatched 

 larvae were measured with an ocular micrometer in a compound, 

 binocular microscope. All lampreys were preserved in a 10 per- 

 cent solution of formaldehyde shortly after capture and measured 

 later; no estimates were made of the probable shrinlcage due to 

 preservation. Churchill (19U5) reports a shrinkage of 3 percent 

 among northern brook lamprey larvae after preservation in 5 per- 

 cent formaldehyde for two months. 



Altogether, U,055 aramocoetes, other than recently-hatched 

 specimens, were collected which presumably were larvae of the sea 

 lamprey. Some qualification of the identity of the species is 

 used advisedly. Five species of lampreys are present in Michigan 

 waters: the American brook lamprey ( Entosphenus lamottenii ), the 

 sea lamprey ( Petromyzon marinus), the Michigan brook lamprey 



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