ME. H. M. BEENAED ON THE CHEENETID^. 417 



gut, they are vacuolated to such an extent as to form a sponge- 

 like connective tissue, the large nuclei being suspended on the 

 threads. The boundaries of the individual cells, however, can 

 still be made out. Without such au arrangement as this, there 

 could be very little free movement of fluids within a body so 

 completely filled up by mid-gut diverticula. The bacteria in the 

 pathological specimen alluded to on the preceding page seem to 

 form nests in these cells (fig. 8). 



Just as the undifierentiated epithelium immediately round the 

 opening of the oesophagus suddenly changes into the large 

 digesting cells above described, so with like abruptness, when 

 the intestine narrows to form the hind-gut, do these cells change 

 into an epithelium of short thick cells with very large nuclei. 

 These line the whole of the portion which I have called the 

 hind-gut, as far, that is, as the enlargement answering to the 

 stercoral pocket of other Arachnids. In the uppermost and last 

 coil of the loop these show signs of being highly amoeboid and 

 vacuolated (fig. 7). Here and there the whole lumen of the tube 

 is found to be filled with two or three cells distended by immense 

 vacuoles, the nucleus being visible simply as a large body sus- 

 pended in a fine membrane. 



Croneberg found no Malpighian tubules in Ghernes Sahnii, 

 and I have entirely failed to find any trace of them in Oiisium. 

 The apparent entire absence of these organs in the Chernetidge is 

 somewhat remarkable, as these tubules are enormously developed 

 in Gihlocellum according to Stecker's description and figures (8). 

 The Chernetidse, on the other hand, are not ill-provided with 

 glands, as we shall see below. "We shall perhaps obtain some 

 insight into the physiological significance of this absence of 

 Malpighian vessels in these animals when we have a tabulated 

 survey of those glands which in the Arachnids serve to remove 

 waste products from the body. I propose to draw up such a 

 list of the glands in the Arachnids in a more comprehensive work 

 dealing with the comparative morphology of the Graleodidse. 



The Circulatory System. 



On account of the minuteness of the heart and the limited 

 supply of material at my disposal, I have been unable to "throw 

 much light on the disputed question as to the number of ostia. 

 Winckler discovered only one terminal pair ; Croneberg finds 



