172 GILBERT C. BOURNE. 
which has appeared above calls into question that great feature 
of animal and plant development which most impresses the 
biological student, viz. that organic growth is a cycle, beginning 
in the single cell, and returning to the single cell again. And 
therefore, in a limited sense, the cell is par excellence the 
unit of life. Its growth takes various forms and shows many 
complexities, but whatever the form, however great the com- 
plexity, it is a progress from the state of an independent 
corpuscle, through a state of many coherent, or continuous, 
or conjunct, interdependent corpuscles, back again to the state 
of a single independent corpuscle. 
This was the great advance made by Remak on the theory 
of Schwann, and summed up in Virchow’s aphorism, which I 
believe to be universally true. For Schwann did not hold that 
cells are the ultimate basis of life: he held that they are 
formed, as a crystal is formed out of its mother liquor, from a 
structureless matrix, the cytoblastema. To some such theory 
Mr. Sedgwick wishes to take us back again, for his “‘ pale and 
at first sparse reticulum ” bears a most suspicious resemblance 
to the exploded cytoblastema. ‘“ The development of nerves,” 
he says, ‘‘ is not an outgrowth from certain central cells, but 
is a differentiation of a substance which was already in 
position.” And earlier in his article, referring to the growth 
and extension of the mesoblast between epiblast and hypoblast, 
he says: ‘‘ What are the facts? The space between the layers 
is never empty. It is always traversed by strands of a pale 
tissue connecting the various layers, and the growth which 
does take place between the layers is not a formation of cells 
but of nuclei, which move away from their place of origin 
and take up their position in this pale and at first sparse 
reticulum.” 
But surely nobody ever affirmed that the space between the 
layers was empty except in the sense that it is devoid of 
cellular structures. It is well known that it is filled with a 
coagulable fluid, and it is worthy of remark that coagulable 
fluids, treated with the reagents now most in use, frequently 
form a reticulum of pale non-staining substance. I can speak 
