Biological Survey — Oswego Watershed 175 



produce the same result. Now when the clogging has gone to a 

 certain extent, the young lamprey fills its branchial chamber, and 

 then closes the branchiopores so that the water cannot escape 

 in the usual way in expiration. Then by a powerful constriction of 

 the branchial chamber the water is forced out of the mouth in a 

 rapid stream which clears away the clogging material. 



This method has been adopted by the sanitary engineers for 

 cleaning their filter beds for water by reversing the current and 

 allowing the dirt to flow off the top. 



Length of Larval Life.—? It is not known how long the young 

 lampreys live in the mud as larvae. The only way to find that out 

 with certainty would be by an experiment in which natural condi- 

 tions were imitated closely and the animals kept from the egg 

 until the transformation. This has never been done. The nearest 

 approximation can be found by seeking the animals from month 

 to month in the mud banks where they naturally live. This has 

 been done for the brook and the lake lamprey in the Cayuga lake 

 inlet, and in the photographs one can see the different sizes 

 and appearance. There is a good certainty for the first season, 

 that is from May and June until Nov.-Dec. (Fig. 5). The brook 

 lamprey is three to four weeks earlier than the lake lamprey 

 hence its young are further advanced. In May and June eggs and 

 larvae may be found in the same nest, showing that some of the 

 eggs were laid earlier than others. It often happens that succes- 

 sive pairs of lampreys use the same nest during the spawning 

 season. This difference in time of laying the eggs also accounts for 

 the difference in size of the larvae of the brook or of the lake lam- 

 prey during the same month ; for example in this figure, Nov. and 

 Dec. 



From a somewhat limited series of sea lamprey larvae and trans- 

 forming ones, the conclusion seems justified that the larval life 

 is precisely like that of the lake lamprey. From the groups of 

 sizes found by Dr. Okkelberg* of the brook lamprey in Michigan, 

 he has, by a series of average curves, concluded that their larval 

 life extends over a period of five years, possibly four years. From 

 my own observations of both the lake and the brook lamprey 

 larvae obtained nearly every month throughout the year, it seemed 

 to me that the time could not be less than four years. 



Wishing to study the structural changes in the various stages of 

 transformation, many large larvae were secured in Aug. and 

 Sept., 1913. These larvae were as long and some of them longer 

 than most of the transforming ones obtained in previous years so 

 that it seemed sure that they would transform during that summer 

 and autumn. They were kept in a large tank with sand and gravel 

 in the bottom and a constant stream of water was turned on so that 

 the conditions would be like that in the natural stream. They 

 were dug up occasionally to see how they were progressing. Some 

 of them commenced to transform in the usual fashion, but to my 



* Loc. cit. 



