370 cook 



obviously different, but the differences are fluctuating or com- 

 pletely intergraded, so that no definite alternatives of descent 

 appear, and no distinct subspecific groups are indicated. 



Individuals are all similar, equivalent and bisexual or her- 

 maphrodite. None of the vertebrate or arthropod animals show 

 this condition, but it appears to be very common among the 

 lower animals and among plants. Species in which there are 

 no specializations of heterism, no differentiated paths of alterna- 

 tive descent, may be called arropic species. 



The arropic condition is not merely synonymous with herma- 

 phroditism, through all arropic species are bisexual. The her- 

 maphroditism of the lower groups of animals and of plants is a 

 normal condition incidental to their more primitive organization. 

 Among the higher groups which have attained sexual differ- 

 entiation hermaphroditism has reference more definitely to ab- 

 normal cases of bisexuality. The arropic condition is also more 

 definite and restricted than bisexuality, since organisms may be 

 bisexual and still manifest some of the following forms of alter- 

 native heterism. 



SPECIES WITH SPECIALIZATIONS OF HETERISM (ROPIC). 



Specializations of heterism exist, and definitely alternative 

 routes of descent are followed by different individuals. The 

 individual members of species fall into distinct groups, but not 

 as the result of segregation or of differences of environmental 

 conditions. The group differences are usually such as to facili- 

 tate or to compel interbreeding between the groups. 



The attainment of the ropic condition marks an important 

 stage in the evolution of a species, very favorable, apparently, 

 to its further development and to the greater and greater exten- 

 sion of the heteric specializations. The distinction is entirely 

 concrete and practical, but there seems to be no suitable and 

 convenient English word by which to designate it. The expres- 

 sions alternation and alternative have been used too widely al- 

 ready, and would increase the confusion now existing as the 

 result of identifying alternation of generations with phenomena 

 of entirely distinct nature, such as the different kinds of cellular 

 structures. 



