166 
Journal of the Mitchell Society [ December 
that is of fundamental importance. If a fairly dense drop of 
the squeezed out tissue be mounted at once and examined with 
a high power (Zeiss 2 mm., comp. oc. 6), the preparation is 
seen to consist of fluid (sea-water) with a few spicules and 
myriads of separate cells. The cells fall into three classes. 
1 The most conspicuous and abundant are spheroidal, 
reddish, densely granular, and about 8/jl in diameter. These 
cells which can be nothing but the unspecialized, amoeboid 
cells of the mesenchyme (amoebocytes or archaeocytes), put 
out hyaline pseudopodia that are sometimes elongated, more 
often rounded and blunt. 
2 There is also a great abundance of partially trans- 
formed collar cells, each consisting of an elongated body with 
slender flagellum. The cell is without the collar, the latter 
doubtless having been retracted. In the freshly prepared tis- 
sue the flagella are vibratile, the cells moving about. Soon 
however the flagellum ceases to vibrate. 
3. The third class is not homogeneous. In it I include 
more or less spheroidal cells ranging from the size of the 
granular cells down to much smaller ones. Many of these are 
completely hyaline, while others consist of hyaline proto- 
plasm containing one or a few granules. 
Fusion of the granular cells begins immediately and in a 
few minutes time most of them have united to form small 
conglomerate masses which at the surface display both blunt 
and elongated pseudopodia. These masses soon begin to 
incorporate the neighboring collar and hyaline cells. One 
sees collar cells sticking fast by the end of the long flagellum 
to the conglomerate mass. Other collar cells are attached to 
the mass by short flagella. Still again only the body of the 
collar cell projects from the mass while there is no sign of 
flagellum. Similarly spheroidal hyaline cells of many sizes 
are found in various stages of fusion with the granular con- 
glomerate. In such a preparation the space under the cover 
glass is soon occupied by innumerable masses or balls of the 
kind just described, between which continue to lie abundant 
free cells, some collar cells, others hyaline. Practically all 
