vin ARTHROPOD A 221 



AEACHNIDA 



Classification adopted 



Delobranchiata Xiphosura 

 f Scorpionidea 



Pedipalpi 

 Embolobrancniata A 



Aranema 



l^Acarina 

 Pentastomida (incertae sedes) 



The most primitive Arachnid living is undoubtedly the horse- 

 shoe crab Limulus, the development of which has been studied by 

 many authors, but most recently by Kingsley (1892, 1893) and 

 Kishinouye (1893). The distribution of this genus renders it unsuit- 

 able as a type of the Arachnida, for it is practically inaccessible 

 to European students. A similar objection applies to the Scorpion 

 which, on the whole, must be regarded as the most primitive of exist- 

 ing land Arachnids ; its absence from the temperate regions of both 

 hemispheres is a serious drawback, and hence we select our type for 

 special description from amongst the ubiquitous spiders, and take as 

 our chief authority Kishinouye (1891-94). This observer has not 

 only published the most thorough work on the subject but has 

 examined the course of development in different genera belonging 

 to different families, and found it identical in all important points. 



AGELENA 



Amongst the types described by Kishinouye there is one Agelena, 

 a cellar spider, representative species of which are found all over the 

 northern hemisphere, and one of which, A. labyrinthica, formed the 

 subject of an embryological research by the late Prof. Balfour. 

 Quite recently another author, Kautsch (1909, 1910), has also studied 

 the development of Agelena labyrinthica. His conclusions in the main 

 confirm those of Kishinouye, but in some points he has penetrated 

 further in the analysis of the development of this species than 

 Kishinouye ; in other points, again, it seems likely that his variations 

 from Kishinouye's account will turn out to be incorrect. We shall 

 therefore select Agelena as a type. The species of this genus can 

 be kept and will breed in captivity. The eggs of Agelena, as of 

 all spiders, are enclosed in a cocoon of silk ; the mother attaches this 

 cocoon to a corner of the cage, and in this way eggs of all stages of 

 development can be obtained. 



Kishinouye had also recourse to a "wolf spider," Lycosa, which 

 spins no web but wanders about in search of prey, and species of this 

 genus are as widely distributed as those of Agelena. Since Lijcosa 

 carries about its eggs in a cocoon attached to the underside of its 

 abdomen, where they remain till the young spiders are hatched, 

 the later stages in development can always be obtained by capturing 



