SCORPIONIDEA. 805 



first ten segments, and two ventral cords which, until they reach 

 the llth segment, bear no ganglia. This and the following six 

 segments have ganglia, the last lying n the 4th metasomatic 

 segment ; behind this, nerves supply the last segment and the 

 post-anal sting. The sense organs are the eyes ; and since 

 ridges exist in some species on the coxae of the pedipalps or of 

 the 1st pair of legs, across which file-like surfaces can be 

 drawn, forming very efficient stridulating organs, scorpions pro- 

 bably have some perception of sound. 



The reproductive organs* are retiform, the annular shape which 

 is common in the Arachnida having become, as it does in Limulus, 

 a network. The ovary consists of three longitudinal hollow 

 tubules united by transverse tubules. It lies ventral to the 

 liver, and is embedded in or closely attached to that organ 

 and is confined to the mesosoma. The oviducts are con- 

 tinuous with the walls of the ovary and pass forward and open 

 by two pores on the genital operculum. The ova arise from 

 certain cells lining the cavity of the ovary the gonocoel 

 and when ripe project into it. They are fertilized in situ and 

 the young scorpion begins its development within the ovary ; 

 after a time it passes into the oviduct and is ultimately born 

 as a miniature of its parent. The scorpion therefore is 

 viviparous and has no larval stage. The testis consists of two 

 lateral tubules connected by transverse ducts. The vas deferens 

 is modified distally to form an intromittent organ and it is pro- 

 vided with accessory glands. The spermatozoa are filiform 

 and motile. The mother sometimes carries the young on her 

 back. 



The features which are mainly used in the systematic study 

 of the scorpions are (i) the presence or absence of a tarsal spur or 

 stout spine on the proximal tarsal segment of the last pair of 

 legs ; (ii) the single or double basal spur which arises from the soft 

 skin between the last and the last but one tarsal segments ; 

 (iii) the nature of the spikes or hairs on the under .surface of the 

 last segment ; and (iv) the shape of the sternum, j" 



Scorpions inhabit warm countries, some species burrowing 

 in the sand. They shun the hot sunshine and live on insects 



* The gonads and their ducts are coelomic ; see p. 317. 

 f In the following systematic account we have followed Kraepelin, 

 Das Tierreich, viii Lieferung, 1899. 



