4 ART. 5. — K. YAtSU : 



together in a palliai sinus and they here have the appearance 

 of a fat-tissue, whose contents have been dissolved out. 



2. Leucocytes. 



Of the second element, the leucocyte, a small number are 

 found in the cœlomic fluid, while a considerable number occur 

 in the marginal lacuna (Randlacune). It is very probable that 

 Semper f6i) observed the leucocytes in the lacuna, which he 

 called the " Lymphraum." Brooks ('78) on the other hand 

 confounded this element with the ordinary blood corpuscles (p. 

 49). The leucocyte measures 13-20 p in diameter, and is some- 

 times spherical in form with a wrinkled surface. It clearly 

 shows amoeboid movements giving off a few blunt pseudopodia 

 and sometimes presenting fine sharply pointed, stiff pseudopodia 

 which cluster together in twos or threes (PI. I., Figs. 3 a, b, 

 and 4). The leucocyte is always found filled with erythrophilous 

 granules, therefore, and treated with erythrosin, gives a very 

 beautiful appearance, as in Figs. 4 and 5 (PI. I.). In some 

 cases a swarm of leucocytes is attached along the epithelial ridge 

 (Epithelleisten) of the palliai sinus (PL L, Fig. 5) : not only do 

 they attach themselves to it, but some of them also force their 

 way into the ridge, probably performing the collection of waste 

 products. This is proved by the following fact. The leucocyte is 

 phagocytous in nature : the yellow pigment, of which more or 

 less is found in the epithelial ridge, is carried out by the element, 

 as shown in Fig. 5 (PL I.) : in the epithelial ridge we often 

 meet with a leucocyte taking up within itself a compact body, 

 which will be described further on : in another case I was able 

 to observe in the palliai sinus a leucocyte surrounding a spindle 



