— 28 — 



Through in-foldings of the coelom the yolk is divided 

 into several distinct masses. The walls of the midgut 

 are in part formed by the ccelom. At its anterior end it 

 is wide, open, and funnel-shaped, and it tapers towards 

 its posterior end. It is everywhere filled with yolk. On 

 the interior side of the funnel formed by the ccelom the 

 entoderm cells have built up an epithelium. This 

 epithelium seems to be separated by a membrane from 

 the walls composing the coelom. 



The cells forming the lining of the midgut have 

 distinct cell-walls; their nuclei stain lightly with hema- 

 toxylin; they are perfectly round, and measure "01 mm. 

 in diameter. A micro-nucleus is often to be found in 

 them. 



The end of the midgut is not in open communication 

 with the rectum, being closed by a plug of entoderm 

 cells. 



The rectum is formed by an invagination of the 

 ectoderm. At its exterior end its cells quite resemble 

 those forming the epidermis, at its interior (proximal) 

 end the cells are vacuolarised. The rectum, as also the most 

 anterior parts of the alimentary canal, is supplied with 

 powerful muscles; one set, the dilators, runs from its 

 walls to the skin of the abdomen ; the contractors being 

 ring-shaped, as in the pharynx and muscle-stomach. 



As in Scorpions the Malphigian tubes are without 

 doubt of entodermatic origin, as they enter the alimentary 

 canal near the posterior end of the midgut. In this stage 

 they are already well developed; they are very long and 

 run parallel and juxta-apposed to the alimentary canal. 



8. The Heart. — The heart of the Pedipalpi has 

 bem best described by Pereyaslawzewa as yet. 



The heart at this stage consists of a long tube, lying 

 dorsally, immediately beneath the skin, in the median 

 plane of the abdomen. Its walls are thick, but do not 

 contain many muscle elements. 



At each segment the heart widens, and seems to me 

 to give off a pair of small arteries. A large artery 

 leaves the heart at its anterior end, this runs into the 



