608 L. H. GOTJGfl. 



sake I shall call such superficial masses of uu-nucleated 

 protoplasm ''surface pits;" this name I give only 

 with reference to their appearance, and not to 

 their structure, and I desire that this may be dis- 

 tinctly borne in mind. The nuclei of the cells of the 

 germ-layer adjacent to this " surface pit " are beginning 

 to arrange themselves radially around the centre of the 

 hollow. Further on, again proceeding forwards, the germ- 

 layer again presents its former appearance. Still proceeding 

 towards the cephalothorax, we meet with another new 

 change. Just before the next thickening containing a 

 " surface pit " is reached, the mesodermatic inner skin 

 begins to lift itself from off the nuclei of the germ-layer. 

 The space between both is now filled with nerve-fibres, the 

 longitudinal fibres being the first to appear, as in Scorpions 

 (Brauer [7]). This "surface pit " only distinguishes itself 

 from the last by the presence of a slight depression on 

 its surface. 



After the next " surface pit " has been reached, the 

 germ-layer loses its continuity and breaks up into a number 

 of groups of cells, each lying in front of its corresponding 

 " surface pit." The space around these groups is filled 

 with nerve-fibres, forming the commissures; they seem to 

 run in every direction. A change has also taken place in the 

 epidermis ; its nuclei are no longer so elongated, having be- 

 come more rounded ; they now measure "01 mm. by '005 mm. 



The first of the groups of brain-germ cells met with 

 measures "08 mm, in length by '02 mm. in breadth, and lies 

 ■02 mm. from the surface of the embryo. It is composed of 

 nuclei lying about three deep and twelve broad, measuring 

 between "009 mm. and "Olmm. They all lie with their long- 

 axes pointing towards the sui^face. The nuclei of these 

 groups are all connected with the centre of the " surface 

 pit" by radial fibres, which all converge towards it. 

 The fibres probably belong to the neuroglia, and serve as a 

 supporting tissue. 



The epidermis is discontinued just at this "surface 



