248 Tait 



abundant in the proximal part of the filament than in the distal part, where 

 the corpuscles can be seen to travel slowly and in single file. In the vein, 

 and still more so in the artery, the movement of the corpuscles is not 

 uniform but jerky, each jerk corresponding to a heart-beat. This can 

 readily be verified by observations on a young specimen (preferably cooled 

 to slow the heart), in which the pulsating dorsal heart is easily visible. 

 In the capillaries again and in the longitudinal vessels at the top of the 

 antennae the corpuscles are carried slowly and uniformly along, sometimes 

 sticking at one spot and then being knocked away again by the impact of 

 succeeding corpuscles. Sometimes in a narrow vessel a row of corpuscles 

 ma}^ be piled up each one in contact with its neighbour : every time a 

 new corpuscle strikes the proximal end of the column one becomes detached 

 from the distal end and floats away. From the fact that the capillary flow 

 is not intermittent one might infer that the venous pulse is due to direct 

 lateral transmission of pressure from the arterial vessel, the whole system 

 being enclosed within a relatively rigid tube formed by the calcareous 

 rings of the filament. 



Except where the corpuscles accidentally come in contact they float at 

 a wide distance from each other in a relatively large volume of plasma. 

 They vary both in size and in form. Generally speaking, they are flattened 

 and somewhat irregular in shape, though showing no processes that might 

 be called pseudopodia. They roll along as they travel, now presenting 

 their narrower edge to view and again being seen on the flat. When 

 removed from the animal and examined with a high power the largest of 

 them are seen full of highly refractile granules which stain deeply with 

 eosin. Other smaller ones contain either basophil granules or clear proto- 

 plasm. In none is the nucleus lobed as is the case in some of the white 

 corpuscles in vertebrates. In all, four or five different varieties of corpuscles 

 can be made out by staining. 



If now, during the time that the circulation in an antenna is being 

 observed, one amputates the terminal portion with a sharp knife, the rate of 

 flow in the artery is greatly increased, while the flow in the vein may cease 

 altogether. The blood meantime pours out at the amputated end, the cor- 

 puscles being washed to a distance in the water surrounding the antennae. 

 If the animal is breathing these corpuscles get washed away in the stream 

 of water continually flowing past the antennae owing to the breathing 

 movements. If the animal is in a narcotic condition and not breathing 

 they settle down on the slide all around the amputated end. Occasionally 

 the plasma is brown in colour, in which case it can be seen pouring out in 

 the surrounding sea-water like smoke from a funnel. 



Some of the corpuscles, however, from the start begin to adhere to the 

 amputated end. At first they stick round the edge of the divided filament, 

 but soon increase in number and form a clump or mass all around the end. 

 The formation of this clump does not immediately stop the flow of blood, for 

 the central part is still kept tunnelled by the rush of outflowing corpuscles. 



