336 ADAM SEDGWICK. 
will find the mesenchyme described or figured as consisting of 
branched, isolated cells. 
Mr. Bourne then refers to certain remarkable researches 
which emphasize the distinction and complete isolation of the 
cells formed in the segmentation of the egg ; with what object 
is not apparent, for he proceeds on the next page to condemn 
those who hold that the organism is constituted of independent 
and isolated units. He even maintains that no reputable bio- 
logist holds such a view. However that may be, I do not 
think that his quotation from Haeckel in support of his con- 
tention is a happy one, for it is perfectly clear from the quota- 
tion that Haeckel, who indeed goes so far as to call the units 
individuals, holds the view which Mr. Bourne condemns. 
Haeckel even calls them individuals of the first order, and 
says that in the adults they frequently unite to form colonies ; 
and he particularly implies that the loss of independence 
caused by their colonial union is secondary. Mr. Bourne 
has completely failed to grasp Haeckel’s meaning, else how can 
he write as he does on the same page with the quotation from 
Haeckel—* So that, as a matter of history, while plants used 
to be considered to be colonies of independent life units, 
animals were not.” 
The most remarkable part of Mr. Bourne’s criticism 
is that in which, after strongly animadverting on my 
statement that it is difficult if not impossible to euunciate 
the cell-theory in a manner satisfactory to every one,—indeed 
he quotes from Schwann and Hertwig to show how precisely 
it can be stated,—he proceeds to devote a dozen or more 
pages of his paper to a consideration of the various views 
which are held and which may be held as to what a cell 
really is! If this amount of discussion is required to arrive 
at the meaning of the word cell, is it likely that there will 
be simple agreement as to the theory which is supposed to 
explain and account for the so-called cellular constitution of 
organisms ? 
Again he says, referring to my description of the embryonic 
mesoderm as a protoplasmic reticulum with nuclei at their 
