772 
ME. H. N. MOSELEY ON THE STRUCTURE AND 
The embryos lie within the ovoid cavities of the uterine tube, quite free and unat- 
tached. They are enveloped in a single very thin pellucid envelope, which encloses an 
ovoid cavity within which the embryo lies coiled up. . 
The earliest stage observed is that shown in Plate LXXV. fig. 1. The embryo is 
worm-like ; the hinder part of the body is coiled up spirally with the ventral surface 
inwards, the anterior extremity being free and nearly straight. The body shows a 
distinct segmentation about its middle, but there are no transverse lines of segmentation 
between the large rounded cephalic lobes and the next segment, nor in the hinder part 
of the body. The three layers of the embryo are already differentiated, and the body- 
cavities closed in. A line following the contours of the body shows the line of sepa- 
ration of the cutaneous layer. The future intestinal tract is represented by a dark 
elongated mass of pigmented matter stretching from a pointed anterior extremity, which 
protrudes within the cephalic lobes, all along the body. The intestine shows bulgings 
corresponding to the segmental elevations of the cutaneous layer. Three rounded eleva- 
tions of the cutaneous layer, marking the commencement of the three first pairs of mem- 
bers, are distinctly to be seen projecting from the under surface of the body on its 
ventral aspect. There is as yet no trace of antennse, and no trace of the mouth was to 
be found. The as yet rudimentary members marked 1, 2 probably correspond to those 
marked 1, 2 in fig. 2. 
The next stage is to be seen in fig. 2. The antennae have budded out and show 
themselves as broad, blunt-ended, unsegmented processes arising from the upper surfaces 
of the cephalic lobes. In rising up from the lobes they carry processes of the cephalic 
cavity with them. In the roof and sides of the cephalic cavity a fold rises up and 
indicates a separation of the cavity into two. The mouth appears as a simple opening 
situate between the cephalic lobes inferiorly, and bounded by a line of thickened tissue. 
The lateral members become more and more developed serially from before backwards ; 
they do not bud off from the end of the body, but transverse lines of segmentation first 
appear between the terminal portion of the body and the already formed members. A 
lateral rounded swelling gradually forms above these lines, becomes more and more 
prominent, and thus forms at last a projecting fold of tissue, the basis of the future 
member. The transverse lines disappear as the members become formed. The second 
pair of members is larger and longer than the rest. The first pair is larger than the 
remainder, and becomes a conspicuous mark by which to determine the identity of those 
on each side of them in further stages. The intestinal tract shows an enlargement at 
its anterior extremity ; it sends out processes of its lateral wall to meet the tissue at the 
interspaces of the feet. Between the first pairs of members it shows a slight bulging. 
There is as yet no anus formed. The lateral undulations or swellings of the body-wall, 
which are the first stages of the limbs, are hollow, a somewhat oval cavity being formed 
between them and a corresponding but opposite inward curve of the digestive tract 
(Plate LXXIII. fig. 9). The undulation of the limb itself is built up of two layers of 
cells, separated by a very distinct line. The inner layer is composed of small rounded 
