592 MALCOLM LAURIE. 



there, in the midst of this granular substance, may be seen the 

 nuclei of free cells. These, probably, play some part in the 

 preparation of the nutritious material for absorption by the 

 embryo, but whether they are derived from the embryo or 

 from the walls of the diverticulum, I have not been able to 

 ascertain, though I think the latter most probable. 



At the posterior end of the body there is a considerable 

 mass of cells, the growth and multiplication of which provide 

 for the rapid increase in length of the embryo. The head 

 end (fig. 10) consists of an almost solid mass of cells, in the 

 middle of which is seen the laterally-compressed lumen of the 

 stomodjeum, which has a highly refractive, probably chiti- 

 nous lining. 



At the sides of the stomodseum the cells have become elon- 

 gated (m), and form masses of muscular fibres, extending from 

 the stomodseum to the lateral walls of the embryo. A pair 

 of solid outgrowths on the ventral surface represent the 

 chelicerse (fig. 10, I). 



No traces of the other appendages are present, and it is 

 noteworthy that this pair of appendages, which in Euscor- 

 pius appears later than the five succeeding pairs, should here 

 be the first to be formed. 



In the next stage only a few points need be noted. Among 

 the most curious of these is the formation of a series of dorsal 

 outgrowths of the body, one to each segment, which give it, 

 when viewed from the dorsal surface, the form shown in fig. 

 11, while in section it has the shape seen in fig. 12. The reason 

 for this curious change in the shape of the body is not clear, as 

 the spaces thus formed are unoccupied by any structures except 

 a few thin bands of mesoblast. A section (fig. 12) shows the 

 gut completely formed as a tube of large cells surrounding a 

 granular mass of food material. The rest of the body-cavity 

 is occupied only by thin trabeculse of mesoblast except on the 

 dorsal surface, where the mesoblast is present in considerable 

 amount and is hollowed out to form the heart. The yolk 

 spheres, which in an earlier stage occupied the body-cavity, have 

 been completely absorbed, and, except for a slight thickening 



