that the ovaries or testes of sonie spent sea lampreys contain 

 spermatogonia (and spermatocytes) or o'dgonia (and o'dcytes), the 

 presence of such germ-cell stages need not necessarily indicate 

 that these speci^iens "would have lived to spaTvn in another 

 season. Weisel (19l|.7) has shotiTi the presence of these germ cells 

 in spent^ land-locked sookeye salmon ( Oncorh;^mchus nerka ) of both 

 sejces. Individuals of this species become seroially mature and 

 spaim only once, dying very shortly thereafter. Weisel concluded 

 that some factor,, other than a potential supplj'" of germ-cells^, 

 limits the spai-vning of this Pacific salmon to a single season. 



In general, the developmental stages of the ova found in the 

 sea lamprey are similar to those found in other fishes that spaim 

 during a single brief period;, i.e.^ the maturing eggs constitute 

 a single size group more or less discrete from, the immature ova. 

 The sea lamprey, ho^vever, differs fundamentally from such fishes 

 in one respect. In females of those species that spaivn in several 

 or many seasons, the immature eggs greatly outnumber the maturing 

 eggs at the time of spasming (Carbine, 19lt.U). It is here demon- 

 strated that in the sea lampreys studied, the maturing eggs out- 

 numbered the undeveloped ones present. This fact, the absence of 

 any germ-cell stages, and the nature of other physiological changes 

 at spaiTning I consider very strong evidence that the sea lamprey 

 spa'tvns but once and then dies. 



Ovum diameters were obtained from seven additional specimens. 

 Six of these were selected from the series available so that one 

 of the earliest and one of the latest migrants and four migrants 

 talcen on scattered inter^rening dates were represented. For 

 miifcrmity these ivere selected to fall within the range of I7.O 

 and 17.5 inches (lj.32 and ul;5 mm.) in total length. These factors 

 only governed the selection of the specimens. A seventh specimen 

 (llo. S-Ul) of comparable length (16. U inches, I4.I7 mm.) talten on 

 the spaivning grounds, was chosen for examination since in this 

 female the bullc of the eggs had burst into the coelom and presum- 

 ably represented fully mature eggs. The data for six specimens 

 are ba.sed on sample sections removed from the previously described 

 midregion of each ovary. These samples vrere teased apart and a 

 random sar.iple of ^00 ova. from each was measured. For specimen 

 No. S-Iil, a random sam^ple of ^00 ova was taken from the total 

 nijmiber that were loose in the coelom. The c!tL^a obtained for all 

 seven specimens are presented in Table 3, and those for six of the 

 3pecimens (including No. S-lil) are graphically portrayed in 

 Figu-re 25. 



Ova from the earliest spawning migrants entering a stream are 

 about 3/u of a millimeter in diameter (average: 0,75 mm., range*. 

 0,l;0-0,85 mm.). Fully mature eggs average about 1.10 millimeters 

 in diameter and range from 0.80 to 1.25 millimeters. l/Iigrants 

 entering the stream on progressively later dates demonstrate pro- 

 gressively more advanced stages of egg development (Table 3). It 



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