GEOGRAPHICAL DISTRIBUTION OF CRUSTACEA. 



species that are higftest in grade, and largest in size. It is headed by 

 the Macrocheira of Northern Japan, the king of all crabs, whose body 

 is seventeen inches long and a foot broad, or, with extended legs, 

 sometimes covers a breadth of eleven feet, and whose anterior legs or 

 arms are four feet long!* The species of the other genera are mostly 

 among the larger of the Maioids, and have no mark of inferiority. 

 Such are the species of Maia, Pisa, Libanii, Eurypodius, etc. 



But among the species of the warmer section, we find the Oncininea 

 and Parthenopinea, both manifestly inferior in grade, the former 

 approaching even the Anomoura, and the latter forming the passage 

 of the Maioids to the Cancroids, as has been explained. We observe 

 also the Periceridse and Tychidae, all very small species, excepting a 

 few Pericerse : the Menaethii, Tiarinise, and Acanthonyces, are examples 

 of the group. In addition, there are the Mithracidse, which although 

 attaining a large size show their inferiority in their shorter epistome, 

 shorter body, which is sometimes even transverse, and their spoon- 

 shaped fingers. In the last character, the Chlorodinae among the 

 Cancroids, similarly show their inferiority to the Xanthidae. That 

 this kind of finger is such a mark of inferiority is apparent from its 

 diminishing in many species as the adult size of the animal is attained, 

 the tendency being towards producing the acuminated finger found in 

 the highest grades. 



We are hence sustained in the conclusion that the Maioids of the 

 Temperate zone are generally those that are highest in grade. It 

 also shows the congeniality of cold waters to the Maioids, that the 

 only Brachyuran peculiar to the Frigid zone is of this group. We 

 refer to the Chionoecetes opilio. 



VII. The Brachyura, therefore, although most numerous in the 

 Torrid zone, do not reach in this zone their highest perfection. On 

 the contrary, the Temperate zone or colder waters are the habitat of 

 the highest species. Hence, as the Maioidea stand first among all 

 Crustacea, the highest development of the class Crustacea takes place, 

 not in the Torrid zone, the most profuse in life, but beyond the 

 tropics and coral-reef seas, in the middle Temperate Regions. 



VIII. The prevalence also of the inferior Corystoids in the colder 

 waters does not invalidate this conclusion, as the fact respecting the 

 Maioids is wholly an independent one ; for these last, by attaining 



* De Ilaau's Fauna Japon., Crust, p. 101. 

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