160 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
found essential to good work, and iron-alum haematoxylin, counter- 
stained with orange G or Bordeaux red proved especially valuable. 
It was necessary to cut sections in both sagitto-longitudinal and 
transverse planes, for, although transverse sections are the more 
generally valuable, the others are essential for purposes of compari¬ 
son and absolutely indispensable in studying the muscles of the 
abdomen. It was found advantageous, though not absolutely neces¬ 
sary, to have in addition to these last, a few corono-longitudinal sec¬ 
tions of each stage. 
External anatomy .— The development of the form of the body 
has already been in the main adequately treated in the preceding 
chapter, while the details of the development of the appendages will 
be better understood from the figures on plates 5, 6, and 7, than 
from any description. It remains, therefore, in this section, to speak 
of the telson and gills only. 
The telson (pi. 7, fig. 31) in the first zoea bears on each side of 
the median marginal notch five feathered spines (1-5), a minute 
bristle (6), and the short, smooth spur of the angle (7); The for¬ 
mula is: 1, 2, 3, 4, 5, 6, 7. In the second stage, a pair of new 
spines (1') are added within the older series. The tips of the uropods 
as they develop, are sheathed within the angle spur (7) and this is 
consequently lost when these appendages, become free. The angle 
spur of the third zoea is a new structure (x). The third and fourth 
stages have the same telson formula: 1', 1, 2, 3, 4, 5, 6, x, and in 
both, spine 4 is short and smooth. The eight setae on the border 
of the telson of the glaucothoe represent spines 1', 1, 2, and 3 of the 
zoeal series. The median cleft appears with the sixth stage, and the 
adult form is attained with the seventh stage. The moderate length 
of spine 4 in the earlier, and its short spur-like form in the later 
zoea stages serve to differentiate the zoeae of longicarpus and 
annidipes from the zoea that I have assigned to acadianus and 
from the larva of the European bernhardus (Rathke, ’42; Sars, ’89), 
in both of which these spines are smooth and elongate throughout 
the zoea phase. 
As already noted, the gills become functional with the glaucothoe 
stage. At this time they are present in the same number and 
arrangement as in the adult crab, viz .: — 
