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SUMMARY OF CURRENT RESEARCHES RELATING TO 
tlie other hand the appendages as well as other organs may be multi- 
plied. Another form of variation is the fusion of the right and left halves 
of the embryo, or an antero-posterior degeneration. The abdomen is 
unusually perfect and well developed in embryos whose anterior portion 
is greatly reduced by median fusion and degeneration. In some cases the 
specimens exhibit what the author calls general progressive degeneration. 
This is probably due, not to external conditions, but to either a general 
or a local lack of formative energy. Four varieties are distinguished : — 
(1) reduction in rate of development ; (2) reduction in size of embryo ; 
(3) local reduction of organs ; (4) reduction in range of development 
of the entire organism, or parts of the same, followed by complete retro- 
gressive degeneration. The result of this is a new kind of death for 
highly organised animals — one, namely, in which the component cells 
gradually decrease in number and in specialisation till nothing remains 
of a once complete organism but a few indifferent cells which, 'in turn, 
themselves disappear by a continuation of the same process. In the 
ease of organs near the apex of the body, such as the olfactory organs 
and the eyes, those on the most anterior segment show the greatest 
amount of median fusion. 
The author next discusses the results of fission, which may be either 
transverse or longitudinal. The former appears to be due to local 
degeneration and median fusion, while the latter is consequent on the 
intercalation of new organs. Double embryos are due to the inter- 
calation of new halves, and new and old halves always match each other 
exactly. It is pointed out that new organs appear in the reverse order 
of their disappearance by median fusion. When new parts are added, 
organs which are morphologically the oldest appear first in the ordinary 
growth, but in the .reverse direction, that is, from before backwards. 
Triple embryos are due to the addition of four new halves to the old 
embryo. Prof. Patten says that various classes of facts and explanations 
have to be harmonised before we can arrive at any explanation of the 
phenomena observed in triple embryos. There is variation in the 
duration of the growth-period of the whole or a part of the organism. 
We may assume this to be due to variations in the inteusity of growth 
or differentiation forces, but not to the lack of formative material. 
There may be an entire absence of certain organs at the outset, and a 
subsequent failure to regenerate the same. This we may assume to be 
due to the absence of specific formative material. General or local 
structural weakness of the embryo is indicated by median fusion of its 
organs in the reverse order of their age and specialisation. The existence 
of large abnormal embryos may indicate forced growth, or an excess of 
formative material ; multiple embryos may be explained in the same way. 
In either case excess of material or excessive growth gives rise to 
the formation of new organs in reverse order of that in which they 
disappeared by median fusion and degeneration. When the formation 
of new organs is followed by degeneration we assume that the multiple 
parts are formed not from an excess of formative material, but by a kind 
of forced growth obtained by drawing from a fixed capital. Multiple 
embryos are probably due to abnormally rapid growth. It is pointed 
out that variation in the growth force is merely a convenient term to 
express the results which follow internally from variations in internal 
