collected at intervals througiiout the migratory and spamiing 

 season (Data are presented in Appendijx G^ Tables 10 and 11^ 

 sexes separately". The proportion of individ-uals displaying 

 the color changes described above at various times during 

 these periods may be derived from these tables) « 



The direct or indirect causes of these color changes In 

 the liver of the sea lamprey are not known » Surface (1899) noted 

 that the livers of spent specimens were green in color and 

 ascribed it to a general accumulation of catabolites. It has 

 been suggested that these color changes result from the success- 

 ive accumulation in the liver of dominant quantities of various 

 bile pigments (bilirubin,, urobilin, and biliverdin) following 

 conversion from one to the other by either oxidative or reduc- 

 tive processes. However^ the sequence of reactions that would 

 necessarily be involved seems someiivhat irrational. Certainly, 

 these color changes in the liver signify a profound alteration 

 in the normal metabolism of the organism iiiiich, perhaps, is 

 associated with the process of sexual maturationo They further 

 signify, if not an actual degeneration of this organ, at least 

 a serious, and possibly irreversible, physiological change in it. 



An. atrophy of the digestive tract of migrating aind spawning 

 sea lampreys was reported by earlier workers (Surface, 1899| 

 Gage, 1928) J I too observed this conditiono Specif icallyj •v^d.t^h 

 increasing sexual maturity and associated cessation of feeding^ 

 the diameter of the digestive tract gradually decreases until, 

 at the time of actual spawning^ it is reduced to a mere hollow 

 thready, one to two millimeters in diameter. 



The digestive tract of the sea lamprey may be likened to 

 a straight tube which travels directly from the mouth to the 

 anus. The regional differentiation of the tract, present in 

 higher vertebrates, is only obscurely indicated. Anteriorly,, 

 a short gastral or stomach zone is pre sent 5 posteriorly, a 

 short rectal sone is more readily distinguishable. Between 

 these lies the intestine which is identified by thicker walls 

 and greater structural rigidity than the other zones possess 

 and by the presen-re of a typhlosole. 



In order to demonstrate the reduction in this organ^ mea- 

 surements Tvere made of the diameters of the intestinal and 

 rectal zones of the digestive tracts of li73 sea lampreys. All 

 measurements were made to the nearest half -millimeter with 

 dividers and a steel rule. The samples utilized for these 

 measurements were collected at intervals throughout the migra- 

 tory season and upon the spaivning beds (Data are presented in 

 Appendix G, Tables 10 and 11, sexes separately. For each sex. 

 the range and average of intestinal and rectal diameters have 

 been tabu.l3.ted first by date of collection and as to whether 

 migrant or spa.wning sea lampreys were examined,, Secondly, 

 these data have been further subdivided and grouped according 



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