- 21 — 



base of the legs of Spiders; they were also described by 

 Brauer (7), who found them in Scorpions. The description 

 and drawings given by Brauer accord with those which I 

 could give for Ad met us. 



(6) The Alimentary Canal. — The alimentary 

 canal is at this stage still very incomplete, only the 

 most anterior part existing as yet. It consists of a simple 

 tube which just pierces the brain. Its outer anterior end 

 does not project beyond the brain, the posterior end 

 doing so for about one-third of its length. From the 

 point where it leaves the brain it is slightly bent in a 

 ventral direction. The cells forming the walls of the 

 alimentary canal form a thick layer at both ends of the 

 tube. No muscles are as yet observed in connection with the 

 alimentary canal. In transverse sections it otherwise presents 

 a similar appearance to that of more advanced stages. 



The cavity of the alimentary canal is Y-shaped; the 

 cells composing its walls are high and cylindrical. The 

 nuclei chiefly lie at the end of the cell nearest to the 

 cavity. A thin cuticle has been secreted by these cells. 



The whole is surrounded by a thin layer of mesoderm 

 cells, which form a skin round the tube. The nuclei of 

 these cells have begun to elongate, and will probably 

 form the ring-shaped muscle found later on in this part. 



7. The Heart. — The circulatory organs are at 

 present represented by the heart alone. The origin of 

 the heart seems to me to be the same as in Scorpions 

 Brauer (7) and other Arachnids. It is evidently formed 

 by the ccelom on both sides of the embryo meeting, 

 leaving a space between the walls on either side, which, 

 although surrounded by coelomatic walls, does not belong 

 to the coelom itself. The heart causes a slight ridge on 

 the surface of the embryo. 



8. The Lungs. — At this stage the lung-books 

 are just beginning to make their appearance. They 

 belong to the first and second abdominal extremities. 

 Laurie (31), however, has located them on the first and 

 third. They differ neither in development nor in appear- 

 ance from the lungs of other Arachnids. 



