NOs 1.) VARIATIONS IN LIMULUS POLYPHEMUS. 65 
The curious pits and sacs just described themselves finally 
degenerate into a mere cloud of cells varying in form and 
appearance, Fig. 89. Many embryos of this kind show slight 
indications of a central depression, probably the last trace of 
a sac like those just described. 
I have found some eggs among those that had been kept alive 
Jor three or four months in which no trace of cells or nuclet was 
visible in surface views, yet they appeared perfectly sound and 
free from decay, even when stained and cleared in clove oil. 
They are probably eggs that have passed so far beyond the 
stages of degeneration shown in Fig. 89, that even the last 
few cells have disappeared. 
There is another series of degenerated embryos that are 
very interesting from their resemblance to the early stages of 
normal embryos. They consist of two groups of cells like 
two primitive cumuli, one corresponding to the head and the 
other to the tail end of the body. This condition has already 
been passed by the embryo shown in Fig. 1. 
Whether or no degenerating embryos as a rule pass through 
this condition with separate Az/agen for head and tail is 
doubtful, nevertheless it is a variety very frequently seen. It 
is well shown in Figs. 72-78. 
There is no way to determine certainly whether an embryo 
like that in Fig. 73 has degenerated, or whether it has been 
kept, by something hindering normal development, in approxi- 
mately its original condition. But the great age of the 
embryo, the evidence in other embryos like this one, of con- 
crescence, and the breaking up of the margin of the circular 
mesodermic area, bears out the assumption that it has under- 
gone profound degeneration. The anterior mass of cells and 
the pit usually seen in its centre probably represent the 
degenerated cephalic lobes and oesophagus, and the poste- 
rior cloud, the anal plate, and telopore. Both of these discs 
are in all this class of cases about the same, but the poste- 
rior one is usually the larger and thicker. Sections of the 
discs show various conditions, from one where there is merely 
a thick, homogeneous mass of cells, flush with the surface, 
but sending into the yolk pseudopodia-like masses of degen- 
