The Structure and Functions of the heemolymph Glands and Spleen. 47 



of three recent observers, dealing' chiefly with those points having- 

 the closest bearing npon the present subject. 



In many text books, as in that of Böhm und Davidoft'^), it is 

 stated that the vascular system of the spleen is open; that is to say, 

 that man}^ small capillaries open directly into what is termed the 

 "spleen pulp", and that veins commencing in a similar fashion, by 

 direct continuity with the interior of the pulp spaces, form the channel 

 by which the blood is drained away. 



Kölliker [9 a], after a number of experiments, in which he made 

 careful injections of the arteries and veins, under different pressures, 

 concludes that the vascular system is closed, or in other words that 

 the blood never leaves the vascular channels. He believes, that in- 

 jections passing into the pulp space, are extravasations, for delicate 

 injections do not enter the spleen pulp, which consists of a string 

 like arrangement, filling- up the spaces between the blood vessels, the 

 veins in particular. 



Weidenreich [19 s] believes in both open and closed systems, 

 occurring side by side; that there is an arterial supply directly con- 

 tinuous with a venous supply by capillaries; while there are in addi- 

 tion arteries and veins, which have direct communication with the 

 spleen pulp.^) 



My investigations lead me to a view hardly agreeing with any 

 of those above quoted. In the first place the Malpighian corpuscles 

 of the sjjleen may in many cases be seen to he enclosed in a very 

 definite endothelium (pi. II. fig. 16), which in all its features resembles 

 that covering the adenoid tissue of a h?emal gland. The spleen pulp 

 may be regarded simply as a large sinus, traversed by an exceedingly 

 dense reticulum and by many trabeculae, which conduct the blood vessels 

 through it. It is true that small capillaries open into the spleen 

 pulp, or rather into this sinus, and that small veins conduct the blood 

 directly away from it. The reticulum of the spleen is composed, as 



') Loc. cit. 



-) Weidenreich also refers to the homology between the spleen pulp and the 

 sinus of a "hsemolymph" gland. This has been noticed by several previous ob- 

 servers. 



