digestive tract in the last two specimens were comparable with 

 that of spent sea lampreys. The fourth lamprey died on 

 September 3 bearing no evidence of a recovery from the degenera- 

 tive changes accompanying sexual maturity. 



This slender evidence suggests that colder water tempera- 

 tures merely prolong the existence of an organism, that, if barred 

 by circumstances from the climactic act of its life cycle ^ is 

 destined to die v;-hen it has burned up its reserves of energy. 



IV. Physical degeneration of migrants and mortality of 



post-spawning adults 



Although the preponderance of evidence presented by earlier 

 investigators (and substantiated 'bj my data) points rather con- 

 clusively to the death of the sea lampreys after the completion 

 of spawning, doubt is still expressed in some quarters as to 

 whether or not this actually occurs. Surface (1899) and Gage 

 (1920) noted an anatomical degeneration of the gut (and liver j 

 Gage, 1928) among migrant and spawning populations of lampreys 

 of this species. Surface (op. cit . ) likewise noted a tendency 

 towards blindness and a shedding of the epidermis among post- 

 spa-wning adults. Both writers refer to the absence of "minute 

 ova" in the ovaries of spent females as evidence that these lam- 

 preys spawn only once and then die. 



If sea lampreys die after spavming, one would expect to find 

 larg-e numbers of dead, spent fish near the spawning grounds. 

 Hoivever, this is not so.; such fish are not seen in abundance. 

 Surface (1899) attributed this dearth to the fact that most dead 

 and dying lampreys were deposited in the deeper, silted pools 

 of a stream and to the fact that immediately after death the 

 lampreys decayed mth great rapidity vmder any circumstances. An 

 experiirient performed by Surface confirmed these contentions. 

 Both Surface (1899) and Gage (1928) noted instances where the pre- 

 sence of the long, tape-like, persistent notochord was the primary 

 e"\ddence :-n the stream, of a post-spawning mortality of adults. 



Gage (1923) pe.rformed ej:periments in holding spawning sea 

 lampreys 'onder various conditions favorable to their recovery and 

 observ-ed that all specimens ultimately died. The most conclusive 

 e-*7idence of mo.rtality in spent lampreys was presented by Sa.rface 

 (1899) for a spawning run of lampreys in a New York stream. He 

 reported that only dead or dying sea lampreys (often badly f ungu-sed 

 and barely alive) drifted doifVnstream to a weir and trap operated 

 on the inlet of Cayuga Lake, New York. 



All of n^ evidence, from both field observations (direct evi- 

 dence) and anatomical studies (indirect evidence), confirms the 

 conclusion that sea lampreys die after spavming once. 



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