50 
Heterotype Karyokinesis and its Significance. 
apparently always occurs, in the heterotype, by means of a trans¬ 
verse breaking of each chromosome. There is considerable difficulty 
in the interpretation of the appearances seen at the actual splitting 
of the heterotype chromosomes, and the authorities are not entirely 
agreed as to the occurrence of transverse breaking in all cases, but 
the mode of splitting is certainly always very different from that 
occurring in the homotype, and its universal interpretation as a 
transverse breaking appears to he at least a possible view. 
Heterotype karyokinesis has been hitherto known only in the 
cell-divisions preparatory to the formation of the sexual cells in 
animals and in those plants which have no “alternations of genera¬ 
tions,” ( e.g . the seaweed, Fucus), and in formation of the spores, i.e. 
the cells which give rise to the sexual generations (gametophyte) in 
those plants which have alternation of generations. 
The discovery which we now owe to Professor Farmer and his 
collaborators is that of the occurrence of the heterotype in the 
dividing cells of malignant growths in the human body. 
In typical “epithelioma” the invading cancerous tissue shews 
a cycle of ordinary somatic divisions. Later on the cells become 
rounded off losing the “prickly” appearance due to the continuity 
of the protoplasm at certain points between adjacent cells, and 
assuming the appearance of embryonic-tissue, well-known as 
characteristic of malignant tumours. In a varying number of 
rather large cells often situated in an ill-defined zone behind the 
growing edge of the advancing “neoplasm” (as the cancerous 
growth is called) the nucleus was seen to have grown to a consi¬ 
derable size. The prophase of division in these cells shewed a 
typical heterotype, the chromosomes being of the characteristic 
form and obviously shewing a reduced number, which could often 
be determined as about half of that shewn in preceding divisions. 
In subsequent divisions the cells of course return to the homotype. 
Other types of malignant growths shew similar phenomena, but 
the heterotype is entirely absent in the so-called “benignant” 
tumours. 
Since the heterotype is, so far as we know, apart from malignant 
tumours, only found at the formation of gametes (sexual cells) or 
the gametophyte (sexual generation) it is proposed to call the neo¬ 
plasms in which it occurs gametoid tissues in order to mark their 
similarity in this respect with gamete-forming tissues. It is impor¬ 
tant to notice that gametoid tissue, though it may be superficially 
similar, has no essential resemblance to true embryonic tissue which 
