DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 513 
fringe of long cilia shown in the figure referred to. These 
cilia belong to the endoderm cells, and are only developed 
upon the first five rows of cells or thereabouts; behind this 
point there is no ciliation at all, nor is the stomodeum 
ciliated. The ciliated cells at the neck of the mesenteron do 
not differ in any way from the other cells of the mesenteron. 
There is an abrupt break between the cells of the stomodeum 
and those belonging to the mesenteron, which is quite obvious 
even when the sections are examined with a low power; the 
stomodzal epithelium is more stained. The cells of the 
mesenteron are laden with spherules and are not stained, 
excepting, of course, their nuclei. The cells of the stomodeum 
are columnar, but much shorter than the cells of the mesen- 
teron. 
The second half of the stomodzum has a muscular invest- 
ment of fibres of some thickness ; this extends for a very short 
distance on to the mesenteron, and gradually disappears. The 
peritoneal investment of the stomodzum is much thicker than 
that of the first part of the mesenteron. The stomodeum 
occupies the first four segments of the body. 
The proctodeum is developed much later; it had not 
been formed in embryos of stage C. It is of much less extent, 
and in transverse sections (fig. 10) is seen ( p.) to lie dorsally of 
the mesenteron. 
§ Epidermis of Mature Embryo. 
In embryos ready to leave the cocoon the epidermis contains 
some peculiar cells. Here and there in longitudinal sections 
through the anterior segments the epidermis appears, when 
examined under a low power, to be perforated ; under a high 
power the arrangement of the epidermic cells at these points 
presents the following appearance. Above the perforation 
lies a large round-cell with a conspicuous nucleus, and below 
this cell is the cavity already spoken of. The cuticle is 
bulged out above the cell. There is no great regularity in the 
arrangement of these cells; they occur sometimes anteriorly 
upon the segment, sometimes posteriorly. The only struc- 
