58 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 
do not see how we can avoid the conclusion that these axial fibers 
of the prism and pyramid cells are somehow concerned in vision. 
In Patten’s theory these fibers would represent a conducting element, 
the real sensory element (fibrils perpendicular to these axial fibers) 
not having been demonstrated by me. 
I have recently read in a short review of Patten’s theory® that 
the evidence we at present have points to the tips of the cones 
(vertebrate eye) as being the seat of the sensation of red. This would 
be exactly the converse of what Patten’s theory supposes. Whether 
or not this objection is a real one, future investigation only can 
determine. 
Hesse" regards the axial fibers that he describes for the rods in 
worms as the primitive fibers of Apathy. In this I agree with him, 
regarding the axial fibers I have described as ‘“ Primitivfibrillen.” 
Further, I believe, if I understand Apathy rightly, that the fibrils 
described by Patten as extending laterally from the axial fibers 
correspond to Apathy’s “ Elimentarfibrillen.” 
It is the long pigment cells that are the puzzling element. Since 
there can be little doubt but that these cells can project and retract 
their pigmented parts (as already described), it would seem that a 
part of their function is to check the diffusion of light in the vitreous 
body when exposed to strong light. This function would be quite 
analogous to that of the pigmented cells of the vertebrate retina, 
which in light become projected between the rods and cones. Similar 
observations have also been made on the compound eyes of arthropods 
by Herrick’? and by Parker’, who find that the distal retinula cells of 
Palaemonetes project themselves distad in the dark, thus surrounding 
the vitreous cones with a cylinder of pigment, while (Parker) the 
pigment of the proximal retinula cells migrates centrad and the 
accessory cells move distad; in light the reverse takes place. Other 
observations of this kind are not wanting for crustacea, insects and 
arachnids. To my knowledge, the pigment changes that I have 
described are the first of their kind for medusae. 
I suggested while describing the capsule, that the lens might be 
adjustable. That the fibers of the long pigment cells extend to the 
lens is my principal reason for this. May these cells not represent 
ganglion cells and their distad fibers nerve fibers? That they are not 
sensory (7. e. are stimulated by light waves) seems to be suggested by 
their not having any axial fiber and in having several centrad pro- 
