596 
later the gradual separation of the syncytial mass into more or less 
distinet cells. Fig. 9 shows a young testis just after the appearance 
of the membrane; the cytoplasm fills the whole space and is not re- 
presented. A few or perhaps often only one of the nuclei at the 
periphery of the syncytial mass or apparently in some cases one or 
more parenchymal nuclei lying near the testis become involved in the 
formation of the membrane. One of these nuclei is shown in Fig. 9. 
At the right of this figure is shown 
the beginning of the vas efferens which 
is formed from parenchymal cells iu 
the same manner as the testis mem- 
brane. 
The ovaries also arise from the 
cells of the parenchyma as was shown 
in the paper referred to above, but 
muscle-cells have not been observed to 
take part in their formation, probably 
because these cells do not usually occur 
in the region where the ovaries develop. 
The greatest care has been taken to avoid error in these ob- 
servations. They have been repeated frequently and with different 
methods and so far as accuracy of observation of small cells is pos- 
sible with present methods of technique the writer believes them 
conclusive. 
If they are correct then the fact is established that germ-cells 
may arise from visibly differentiated somatic cells. Other probable 
cases of the same sort exist, but because the striking transformation 
of the muscle-cells into testes is one which leaves little room for doubt 
it seemed worth while to call attention to it since the matter is of 
considerable theoretical importance. 
As regards the development of the testes in general in Moniezia 
it seems almost impossible to avoid the conclusion that certain cells 
develop into germ-cells not because of any inherent properties by vir- 
tue of which they differ from their fellows but because they are sub- 
jected to certain conditions in the organism. 
The following facts: the relatively sudden appearance of the testes 
in a zone extending across almost the whole width of the proglottid, 
and nowhere else; the apparent absence in this zone of special cells 
destined to give rise to testes; the development of the testes from 
cells in this zone which were previously differentiated parts of the 
soma and not visibly different from somatic cells in other regions; and 
Fig. 9. 
