395 
papillae are free, however, and so the structures will be spoken of 
as evaginations. By webs are meant the connecting plates of tissue 
that arise from the main body of the electroplax and at the same 
time connect two or more papillae (Fig. 5, 76). By strands are meant 
the connectives that reach from papilla to papilla without touching 
the plate portion of the electroplax (Fig. 5, 77). Fig. 9 shows a 
section taken horizontally through the papillae at a point near their 
bases and shows the strands and webs also. Fig. 11 shows a section 
taken in the same plane but near the tips of the papillae which appear 
as small areas of somewhat rounded form (Fig. 11, 25). 
Marked variations are apparent in the comparative width of the 
papillae and the closeness with which they are set on the surface of 
the electroplax. On a certain electroplax they may be twice as wide 
and set three times as far apart as on another and there is in most 
cases a certain distinctive air about an electroplax that marks it from 
its fellows and divides the whole number of them into groups. Fig.5 
and 6 show two examples of the condition in the large majority of 
cases, while Fig. 7 and 8 show two extremes such as are found in a 
few cases. 
The cytology of the electroplax is most interesting and cannot be 
easily compared with that of any | 
other form. The following descrip- 
tion must of necessity be very 
weak and incomplete on account of 
the condition of the material which 
has been mentioned above. The 
Fig. 9. Horizontal seetion through 
‚the bases of the papillae. The webs con- 
nect the bases of the papillae so continuously 
that the section is that of a series of in- 
vaginations rather than that of a number 
of evaginated papillae. 19 lymph channels. 
The numerals indicate the same as in the 
preceding figures. 
species dealt with here is A. guttatus, the more northerly of the two 
east coast species as well as the rarer. 
Inside of the bounding electrolemma, which is a very delicate and 
homogeneous membrane much like the sarcolemma in the muscle cell, 
the cytoplasm is arranged in three horizontal layers which are not so 
well defined from one another as are those in the electroplax of Raja 
for instance. The upper of these layers (Fig. 5 etc., 9) is very thin 
and contains an evenly-spaced series of nuclei, round in horizontal 
outline, flattened to fit the layer and placed closely in the layer at 
