EARLY DEVELOPMENT OF JULUS TERRESTRIS, 461 
mesenteron. They are divided into ganglia, one pair being 
present for each segment of the body; from each ganglion a 
nerve is given off to the corresponding body segment. The 
sub- and supra-cesophageal ganglia are almost formed. 
The splanchnic layer of mesoderm covers the mesenteron, 
the stomodeum, and proctodeum. The median part of the 
somatic mesoderm lies above the nerve-cord, between it and 
the gut; from thence it passes downwards to the body wall. 
This arrangement is shown in fig. 34, which is a transverse 
section through an embryo of the twelfth day. 
Within the yolk, which is still present in great quantity in 
the body-cavity, there are present a number of cells remaining 
over from the hypoderm after the formation of the mesodermic 
keel, and the mesenteron. These cells eventually give rise to 
the circulatory system, to the muscles of the segments, in part 
at any rate, and to other muscles ; they are therefore mesoderm 
cells. The lumen of the mesenteron is now continuous with 
that of the stomodzeum and of the proctodzum. 
Fig. 14 shows a longitudinal vertical section through an 
embryo of this age. 
On the twelfth day the Malpighian tubes grow out of the 
proctodeum. Their lumen is from the first continuous with 
that of the proctodzum. They end blindly and are enveloped 
by the splanchnic mesoderm. 
Fig. 34 is a transverse section through an embryo on the 
twelfth day. The section is taken through a ganglion in the 
posterior part of the body. It shows the two ganglia united 
by a narrow median part and each giving off a nerve to the 
ventrai part of the body, where the rudiments of a pair of 
limbs can already be traced. The Malpighian tubes are also 
shown. This section also shows the body cavity divided into 
four compartments by means of thin layers of mesoderm. 
Late on this day the animal is hatched with only the rudi- 
ments of its appendages, and I propose to reserve a full 
description of the stage till a future time. 
VOL, XXVI, PART 3,—NEW SER, H H 
