582 
J. S. KINGSLEY. 
continuous and not differentiated from the epiblast, although 
it has become separated in the anal region (fig. 46). In the 
middle region the broad bands on either side extend into the 
legs (fig. 47), but no trace of a coelom has yet appeared. On 
the neural side of the limbs it is a single cell thick, but in the 
region of the appendages it is much thicker. This thicker 
portion soon splits into somatoplure and splanchnoplure, and 
the resulting coelom extends into the legs (fig. 30). It is to 
be noticed that the ccelomic cavities are separate, one being 
formed to each segment on each side, and further, that each 
metameric cavity forms at first as several parts which afterwards 
unite. In the stage of fig. 6 the mesoblast has extended itself 
to the edge of the carapax where it thins out, the coelom 
not reaching quite so far. ' In a slightly later stage (fig. 34), 
but still not far enough advanced to be equal to fig. 11, longi- 
tudinal sections show larger coelomic cavities, eight in number, 
one for each segment developed. 
The mesoblast gradually extends itself upwards on either side 
until at the stage of fig. 12 (fig. 21) it meets as a single layer of 
cells iu the dorsal region. On the dorso-lateral region it forms 
a longitudinal band-like thickening (fig. 21, m ), the earliest 
appearance of the extensor muscles and the points of attach- 
ment of the muscles of the limbs. At the same time on the 
ventral surface of the body, either side of the median line, 
portions of the mesoblast grow up into the yolk, dividing it 
into segments (fig. 22, mp.). By this segmentation, as shown in 
the section just referred to, we have conclusive evidence that 
the metastoma (chilaria) is not to be regarded as a morphological 
appendage, since both it and the sixth pair of legs arise from 
the same segment. This was more than suspected by Professor 
Lankester, and is an important point in the series of homo- 
logies he has suggested between Limulus and the Scorpions. I 
might incidentally mention that embryology affords not the 
slightest evidence of the missing abdominal segments needed 
to render the correspondence between the two exact. 
These septa not only furnish the boundaries between the 
segments, but they also give rise to the muscles of the appen- 
