MR. J. F, BULLAR ON THE DEVELOPMENT 
514 
a constriction, and appear to pass through the pigmented membrane (Mbn.) which 
is parallel to the external surface of the eye. Extending from this membrane to 
the cuticle, and separating the different divisions of the eye from each other, are a 
number of pigmented connective tissue partitions (C.T.). These parts are shown in 
transverse section — that is, in a section made parallel to the surface of the eye — 
in fig. 13, which represents a single complete division and parts of the partitions 
(C.T.) dividing it from the six adjacent divisions. The circle (X) marks the position 
of the kristal Jcegel as it would be seen if the focus were adjusted to a point slightly 
above the level of the paper. Below this are the seven cells (Z) arranged so as to 
radiate like the spokes of a wheel from the centre of the kristal keg el ; each cell at its 
inner edge contains a small transparent unpigmented body ( Sehstdbchen ). 
Following these cells (fig. 14, Z) towards the brain they pass through the mem- 
brane (Mbn.), run on sej)arately for a certain distance, and then all coming into close 
contact, become again constricted and pass into a fine bundle of nerves (figs. 12 and 
14, Z") which soon becomes lost in the fibrous tract marked Op. T. (fig. 14). 
All the parts of the eye external to the membrane (Mbn.) are developed from the 
epiblastic thickenings. Whether the parts internal to this, marked Z' and Z ", are 
developments from the epiblast, from the cerebral ganglion, or from both, I have not 
been able to determine. 
In the fifth stage the external appearance is much the same as before ; the head and 
abdomen are a little more distinct, and the limbs have increased in size, the antennee 
now covering the mouth appendages. A little pigment has appeared at the posterior 
border of the eyes. 
The segmentation of the ventral nervous system is now complete, and there are 
sixteen distinct ganglia ; these are well shown in fig. 15 : a longitudinal section. 
The two fibrous cords extend to the posterior end of the nervous system, and the skin 
is now entirely separated from the ganglia. 
The mouth and oesophagus are very narrow ; the stomach has become larger, and 
two projections have appeared in its floor. 
The hind-gut extends forwards as far as the anterior edge of the fourteenth ventral 
ganglion. Its anterior end is still closed. 
The liver coeca are a great deal larger than in the last stage, and have come into 
contact with the fore-gut. 
Above the hind-gut, and extending beyond it in front as far as the tenth post oral 
ganglion, and therefore occupying the same position as in the adult, is the heart. Its 
walls consist of elongated nucleated cells. From its anterior end a band of cells 
passes forwards to the dorsal surface of the embryo, and from about the middle of its 
ventral surface another band passes to the anterior end of the hind-gut. Posteriorly 
it is attached to the dorsum and to the anterior ventral wall of the telson. 
The dorsal organ has enlarged a little, but otherwise remains the same as iii the 
third stage. 
