No. 2.] ANURIDA MARITIMA. 281 
consideration of the sizes and shapes of the eggs in the three 
forms. In Lepisma the egg is a regular oval, and about I mm. 
in its longest diameter; in Campodea the egg is spherical, and 
has a diameter of about 0.4 mm., while the egg of Anurida has 
also a spherical form, but is only about 0.27 mm. in diameter. 
This increase in size is enough to explain the loss of holoblastic 
cleavage in the larger forms, considering its imperfect preser- 
vation in the small anuridan egg. 
The process of germ band formation as described by Uzel 
for Campodea agrees very closely with the corresponding one 
in Anurida. A “dorsal organ” is described as having a posi- 
tion comparable to that held by the precephalic organ in 
Anurida. There are in Campodea no embryonic membranes 
corresponding to the amnion and serosa of the pterygote insect. 
In Lepisma these structures appear, but the amniotic sac re- 
mains open for a short distance. In many ways Campodea 
suggests to Uzel the myriapod type of development. 
In the more complete consideration of Lepisma by Heymons 
there are several special points of interest. He finds rudi- 
mentary appendages upon the tritocerebral segment, which 
eventually disappear in early embryonic life. In discussing 
the origin of the mesenteron, several observations agree closely 
with those made on Anurida. The appearance of this part of 
the alimentary tract is very much delayed. Not until after 
hatching is it definitely formed. Unfortunately, certain criti- 
cal stages were not found; but the author saw in late embry- 
onic stages small groups of cells taking up a peripheral position 
on the yolk. These groups increase by rapid division originat- 
ing from what the author considers yoke cells that have been func- 
tioning throughout embryonic life in the assimilation of yolk. 
Hence he says the mesenteron is truly entodermic in origin. 
There is only one principal point of difference between this 
view and the one given for Anurida. In the latter case, it is 
clear that the mesenteron arises from cells originating at the 
same time as the yolk cells, but remaining latent through the 
early embryonic stages; the yoke cells themselves degenerate 
at the close of embryonic life. Possibly there is some such 
latent source in Lepisma that may have escaped observation. 
