442 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
vacuolization of the surface of the epidermis, brought about artifi¬ 
cially in decalcification, was thought to indicate special localized 
states of the epidermis. 
As shown in figures 12, 13 (pi. 44), and 15 (pi. 45), the connective- 
tissue mass of the annulus is a variable mesh of strands and plates 
containing scattered nuclei and continuous with the epidermis. The 
spaces of this net were full of blood represented in the sections by a 
finely granular precipitate and by a few free cells. 
We thus find that the annulus is merely a conical syncytial mass 
full of blood and covered over by a special exoskeleton, and it seems 
that its usefulness as a sperm reservoir pertains to the cavity within 
the inert exoskeleton while the form-determining factors that make 
it useful, presumably reside in the living syncytium, or in other parts 
of the bodv, and not in the exoskeleton. 
Having described the structure of the annulus we must next empha¬ 
size some facts in regard to its symmetry. While the annulus lies 
across the median line in such a way as to be balanced right and left 
in general form, yet there are some interesting departures from the 
bilateral symmetry characterizing median plates and protuberances 
in Crustacea. The foregoing figures show that the two tuberosities 
are not alike; one only has a spur passing across the median plane 
toward the other; the trumpet is so bent that the part on the right has 
no like fellow opposite on the left; the orifice is entirely upon one side 
and the recess though lying across the median line has one side larger 
than the other (pi. 43, fig. 8). Again, the zigzag suture and the curved 
.slit passing from it to the cavity of the trumpet are not balanced right 
and left (pi. 43, figs. 1, 5). 
In all parts of the annulus there were individual differences but the 
asvmmetrv above noted, was found in all individuals examined. 
In the majority of specimens examined, the orifice was upon the right 
side of the animal while the tuberosity on the left sent its spur across 
to the right tuberosity (pi. 43, figs. 1, 5). The zigzag suture then gen¬ 
erally passed as in figure 5, but with individual differences in length, 
straightness, and angle of the three successive lines, which may pass 
over into one another so as almost to form a sinuous, in place of a 
zigzag line. In some the left side of the recess may be the longer (pi. 
43, fig. S) though in others the right side may be the longer, and 
yet the orifice may be on the right side in each case. 
But while the majority of the crayfish examined were, as we might 
