THE EMBEYOLOGY OF A SCORPION. 185 



muscles of the body. The inner layer becomes folded so as fo 

 surround the liver and intestine, and the coelomic space becomes 

 partly filled up by trabecular tissue. 



Conclusion. 



The development cf this Scorpion, of which I have tried to 

 give an outline above, is interesting in many points. It does 

 not agree closely with any other Arachnid type as yet described, 

 and I have for the present given up all attempts at comparison. 



The development of the central and lateral eyes entirely bears 

 out Lankester and Bourne's description of their structure. It 

 is true that the central eyes are three-layered, but as the retina 

 is the second layer from the surface — the third layer forming 

 only a post-retinal membrane— they may be called diplostichous. 

 The account given above of their development agrees in all 

 essential respects with that of Parker, but, having a larger 

 supply of embryos, I have been able to trace the earlier stages 

 and the connection of the eyes with the cerebral invagination. 

 Their mode of origin resembles very closely Locy's^ description 

 of the development of the eyes in Agelena nsevia, the chief 

 difference being that in Agelena the optic invaginations appear 

 to have no connection with the formation of the brain. Locy 

 does not, however, give a detailed description of the formation 

 of the latter. 



The description given above of the development of the lateral 

 eyes also agrees pretty closely with that of Parker. In these, 

 as in the central eyes, Lankester and Bourne's conclusions are 

 confirmed, and Patten^s- conclusions as to what the structure 

 of the eyes must be in order to fit in with his theories are 

 shown to be without foundation. The lateral eyes are mono- 

 stichous, being simply somewhat specialised hypodermis cells. 



The mode of formation of the ventral nervous system is 

 exceptional among Invertebrates, resembling rather that of 



^ ' Bull. Mus. Comp. Zool., Harvard,' vol. xii, p. 85. 

 - "Eyes of Molluscs and Arthropods," 'Mitth. Zool. Stat. Naples,' 

 Bd. vi. 



