1100 The American Naturalist. [December, 
ectoderm or entoderm ; the idioplasm is not early divided qualitatively 
amongst the cells as Raux and as Weismann maintain. This same 
lack of differentiation is shown, the author holds, by certain other 
abnormalities sometimes produced when the embryos are subject to the 
action of lithium. Thus larve may be reared in which the arms and 
ciliated band are formed in abnormal places, from cells, apparently, 
which would not normally form such structures at all, i. e., cells have 
been induced to form what they would not be able to form were they 
really specialized. 
From the wealth of observation upon the action of lithium at differ- 
ent stages of larval life exposed for different periods to this action we 
can select only one of the interesting facts that result, namely, that the 
action of this salt does not cease when the egg is removed from the 
salt into pure sea water. Under some conditions such eggs may continue 
to develop along the abnormal direction or may begin to form lithium 
larvæ, though as far as can be seen they are perfectly normal when 
removed from the salt into the sea water. Such facts militate against 
the author’s former assumption of the direct action of these salts in 
modifying the osmotic penetrability of the egg protoplasm and show 
that the action is a more subtle, unknown one. 
The author argues that the entoderm cells of the blastula have the 
property of taking up and holding the lithium salt to a greater extent 
than do the ectoderm cells. In some unknown way this is connected 
with their unusual mode of growth. 
It is important to note that the eggs of different individuals react to 
quite different extents, different degrees, to the stimulus produced by 
the same amount of the lithium salt. 
Mechanics of Embryology.—Hans Driesch? adds four more. 
chapters to his six previous contributions to this subject. 
The first treats of the results obtained when the eggs of Spheerechi- 
nus are put, about twenty-six hours after fertilization, into water that 
is kept fur eighteen hours in a warm chamber heated at 30° C. 
The larve that result are blastulas with a protruding tube on one 
side; in fact the increased temperature has brought about the same 
result as Herbst obtained by the use of lithium salt, the gastrulations 
begin in an inverted sense, the entoderm grows outward instead of 
inward. Such exogastrule when removed to cooler water continue to 
live and may form plutei with long entodermal tubes attached; in each 
case the entodermal tube, or more properly closed pouch, is divided 
5Mitth. Zool. Station Neapel II. 1893. 
