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question of spontaneous generation, which has for so long a 
time been bound up with the question as to whether a cell can 
take origin independently of a pre-existing cell, becomes 
now an inquiry as to whether it is possible artificially to en- 
gender plasson, and to cause vital phenomena to appear 
therein. It is quite certain that the Monera—simple frag- 
ments of plassic matter—manifest their vitality quite as do 
the most elevated organisms by the phenomena of nutrition, 
of multiplication of movement, and of irritability. 
Every small living mass of plasson is a cytod, and the 
cell differs from the cytod in that a nucleus is differentiated 
in its interior from the surrounding matter. It clearly results 
from the theory of evolution, that plasson must have existed 
before monocellular beings, and the latter take their origin 
in cytods. 
The ontogenetic evolution of the Gregarine represents 
the history of the genealogical or phylogenetic development 
of the cell. The psorosperms give rise to the globules of 
plasson, devoid of all nucleus, vacuole, or membrane ; they 
may be compared to the simplest Monera. The Gregarine 
are originally then simple naked cytods (Gymnocytods). 
But soon a clearer and denser peripheral layer appears around 
the cytod, whilst the central part of the globule remains 
formed of a more fluid and more granular plasson. The 
Gymnocytod tends to elevate itself above the Monera, which 
are always devoid of a cortical layer; whilst we find regu- 
larly such a layer in the Protoplasta, viz. the Rhizopods, the 
Myxomycete, and above all, in the Infusoria. In speaking 
of Protomyxa aurantiaca (see this Journal, 1869), Haeckel 
says clearly, ‘‘ Nothing is to be observed of a separation into 
a thicker cortical layer and a thinner fluid medullary layer, 
as is found in many Rhizopods and Myxomycete.” 
But the Gregarina in course of development remains still 
in the cytod condition, and on the surface of the cytod the 
two pseudofilaria develop as buds formed at the expense of 
the material of the cytod, as described above. In the gradual 
formation of nucleolus, nucleus, and cortical substance, we 
see a gradual differentiation and localisation of chemical ele- 
ments, primitively united in the plasson of the cytod. 
There is not a general agreement as to what must be 
understood by the endogenous multiplication of cells. It 
has been long admitted that endogenous generation consists 
essentially in the division of the cellular contents without 
the cell-membrane taking part in this division ; but since we 
have learnt the true nature of the cell-membrane, we know 
that it never takes part in the process of cell-division. ‘The 
