GERM-CELL HISTORY IN THE BROOK LAMPREY 73 



planeri. Among these 10.3 per cent were undifferentiated, 16.3 

 per cent older undifferentiated (probably young testes), 48.9 

 per cent true ovaries, and 24.5 per cent mixed glands. He came 

 to the conclusion that the greater part of the hermaphrodite or 

 mixed glands " . . . wird als mannliche Anlage gelten kon- 

 .nen, in der eine kolosale, gleichsam atavistische Anlage von Eiern 

 stattfindet." He states further: ''Es ist anzunehmen, dass diese 

 Eier spater wahrend oder nach Metamorphose der Rtickbildung 

 anheimfallen werden." 



I published ('14) a summary of some work on the sex glands 

 of the American brook lamprey, Entosphenus wilderi. Fifty 

 larvae ranging in length from 20 to 75 mm. were examined for 

 sex. Out of these 46 per cent were regarded as female because 

 the germ glands contained practically nothing but growing 

 oocytes, 10 per cent were taken to be true males on account of 

 the absence of any growing oocytes in the germ gland, and 44 

 per cent were considered intermediates, for the reason that both 

 cysts and growing oocytes were found in the glands. Since in 

 the adult stage males and females occur in nearly equal numbers 

 and since undeveloped oocytes were found in the adult testes, 

 the conclusion seemed warranted that the intermediates became 

 males. 



Two other instances are recorded in which oocytes were found 

 in the mature testis of the lamprey. Beard ('93) found in the 

 testis of a specimen of Petromyzon planeri one well-marked oocyte 

 in an individual folhcle for every forty sections of 10 /x thickness. 

 Ward ('97) describes the occurrence of a single microscopic 

 oocyte in the testis of an adult Petromyzon. 



Further discussion of juvenile hermaphroditism in lampreys 

 will be found at the close of the next section following the discus- 

 sion of like conditions in other vertebrates. 



e. Other cases of juvenile hermaphroditism among vertebrates. 



Cyclostomes. Cunningham ('86) found that in all specimens 

 of Myxine glutinosa with very immature eggs, the caudal portion 

 of the sex gland had the structure of a testis. In one specimen 

 this testicular portion showed spermatogenesis and a number of 

 spermatozoa. In all the sex glands of specimens with well- 



