New Forms of the Hemichordata. 169 



corpuscles accumulate in the distal or lophophoral region, from 

 which they are finally expelled by a strong contraction of the 

 median vessel into the general vascular system, there being thus 

 a circulation of blood corpuscles but not of plasma. I have also 

 observed something similar to this in specimens of P. capensis 

 which have been removed from their tubes, and also similar move- 

 ments in the vascular system of individuals which have thrown off 

 the lophophoral region, with the exception in this case, of course, 

 that the blood corpuscles, while accumulating at the distal or 

 regenerating end, cannot pass off again by a circulatory movement 

 into the system. 



I cannot but suspect that these interesting phenomena observed 

 by Enriques, are mainly due to injury or irritation produced in 

 removing the animal from its tube, and might be compared from 

 their mechanical aspect at least to clot formation. 



The method adopted in making the following observations was to 

 select for microscopic examination specimens projecting over the 

 edge of a piece of stone so that they can be examined by transmitted 

 light. The animals sooner or later began to expand, often to a very 

 considerable extent, and an account of their habit of occasionally 

 rotating slowly in the tube, first in one direction then in another, 

 presented different aspects of the vascular system. The method is 

 rather tedious, but probably ensures normal results. 



On the first protrusion of the tentacles, the movement of the blood 

 was readily observed in a few, and, in full expansion, blood was seen 

 to course up and down in all the tentacles. The intervals between 

 such pulsation varied much (4-10 seconds). The inflow of the blood 

 into the blood-vessels of the tentacles was slow, and apparently 

 caused by pressure from behind ; the outflow was more rapid and 

 apparently caused by contraction of the vessels. 



The inflow and outflow of blood was never synchronous in all the 

 tentacles, but was irregular, though occasionally a few neighbouring 

 tentacles showed pulsation at the same time. Each of the blind 

 tentacular vessels opened into a common circular vessel in which 

 the course of the blood was sometimes in one direction, some- 

 times in another. 



Two such circular vessels were seen lying not far from each other. 

 These were, however, not recipient and distributing vessels such as 

 occur in P. australis (2), but were merely the single connecting or 

 circular vessels of the inner and outer circle of tentacles. In both, 

 the movement of the blood was to and fro without any regularity. 

 The outer circular vessel was continued round on the oral side, but 



the inner circle was interrupted at this point thus 



