656 ZOOLOGY. 



of northern forms, and alpine " species " proving to be va- 

 rieties or seasonal forms of lowland species. For example, 

 Weismann states that the European butterflies, Z^/caow amyn- 

 tas and polysperchon, are respectively summer and spring- 

 broods. Anthocharis Simplonica is an alpine winter form of 

 Anthocharis Belia, as is Pieris bryonm of Pieris napi. In 

 this country, as Edwards has shown, two of the polymorphic 

 forms otPapilio Ajax — i.e., Walshii&udi Telamonides — come 

 from winter chrysalids, and P. marcellus from a second 

 brood of summer chrysalids. It thus appears that poly- 

 morphism is intimately connected with the origin of species. 

 Perhaps the most remarkable case of polymorphism is to be 

 seen in the white &n.is\Termites), where in one genus there 

 are two sorts of workers, two sorts of soldiers, and two kinds- 

 of males and females, making eight sorts of individuals ; in 

 the other genera there are six. Among true ants there are, 

 besides the ordinary males, females, and workers, large- 

 headed workers. In the honey-ant [Myrmecocystus Mexi- 

 canus), besides the usual workers, there are those witL 

 enormous abdomens filled with honey. Other insects, es- 

 pecially certain grasshoppers, are dimorphic. Certain par- 

 asitic ^Nematode worms are dimorphic ; and among the- 

 Coelenterates, especially the Hydroids, there is a strong ten- 

 dency to polymorphism. 



Individuality.— Perfect individuality among animals is. 

 the rule, each individual being capable of maintaining an 

 independent existence ; but we have seen that there are many 

 of the lower animals in which it is difficult to determine 

 whether the different members of a colony are really in- 

 dividuals or simply individualized organs. 



The student, in referring back to the account of the Por- 

 tuguese man-of-war, will find it diSicult to say whether the 

 four kinds of members of the floating colony are organs or 

 individuals, and he will probably agree with the view that 

 it is best to provisionally call them zooids or individualized 

 organs ; for the feeders, the reproductive zooids, the' digest- 

 ive zooids, and the swimming float, or the swimming bells 

 of the other Siphonophores, are higlily specialized organs, 

 and only differ from true individuals in lacking the power 



