SOME POINTS IN DEVELOPMENT OF SCORPIO PULVIPBS. 595 



latter are the nuclei of the retinal cells, and as from the dis- 

 tribution of the pigment special pigment-cells seem to be 

 present, the large spherical nuclei probably belong to these 

 latter. Absolute confirmation of this view by dissociation of 

 the elements of the retina has unfortunately proved impossible, 

 owing to their state of preservation. 



Conclusions. 



The development of this form adds another to the numerous 

 types of development in the Arachnida. It is, as is shown 

 by its mode of nutrition, a highly specialised form. There is 

 no doubt that the type of development represented by Eu- 

 scorpius is the more primitive of the two. The chief argu- 

 ments in favour of this view are the formation in Scorpio 

 fulvipes of (1) a rudimentary amnion, and (2) the formation 

 of yolk spheres in the earlier stages, and a mass of yolk round 

 which the gut is formed. 



Further, so far as can be made out from the description by 

 Kowalewsky and Schulgin,i the development ofAndroctonus 

 follows much the same lines as that of Euscorpius. It is 

 curious that Euscorpius should resemble the very distantly 

 related Androctonus so closely, while diflFering so markedly 

 from a comparatively near relation like Scorpio; and further 

 study of the mode of development in other forms would, pro- 

 bably, throw an interesting light on the value of the present 

 system of classification. 



The mode of nutrition explains many of the peculiar points 

 in the growth of the embryo, everything being sacrificed to 

 the rapid development of the organs — chelicerae, stomodseum, 

 and gut — necessary for nutrition, and the other appendages, 

 together with the mesoblast and nervous system, being formed 

 at leisure after nutrition is provided for. 



I have, unfortunately, not been able to find the remarkable 

 sense organs described by Patten.^ 



' ' Biol. Centrlbl.,' vol. vi, p. 525. 



' ' Quart. Journ, Micr. Sci.,' vol. xxxi. 



