THE ANATOMY AND DEVELOPMENT OF PERIPATUS NOVAE-BRIT A.NNIAE. 47 



the fact that, pari passu with the growth of the embryo, a decrease in the size of the 

 trophic vesicle supervenes. From specimen II. 



Fig. 33 a. Another embryo closely similar in point of age to the preceding. This figure 

 is inserted chiefly for the purpose of elucidating the preceding figure and the remarks made 

 upon the latter. It shows the independence of the posterior abdominal region. The trophic 

 vesicle is only directly connected with the anterior abdominal and cephalic regions. The 

 knob-like or funnel-like stomodoeum (the dark-shaded body behind the antennae) projects 

 vertically into the trophic cavity. The embryo is doubled up by a ventral abdominal flexure, 

 and the caudal end projects far in front of the cephalic end. The trophic vesicle is restricted 

 to the anterior moiety of the embryo of which it forms the back. Thus in this region the 

 wall of the trophic vesicle is the dorsal side of the embryo. The trophic cavity is continued 

 into the free posterior moiety of the embryo, but its proportions are so narrowed that the 

 dorsal side of the embryo in this region is not inflated as it is in the anterior region. The 

 ventro-lateral margins of the body are thickened by the appendicular outgrowths which contain 

 mesoderm and by the delaminating nerve-cords. The latter appear as distinct parallel ridges 

 bounding the sides of the body. Between the neural ridges the ventral body-wall is as thin 

 as the wall of the trophic dilatation, so that between the neural ridges there is a wide 

 longitudinal groove which is seen very clearly by focussing deeply through the trophic wall. 

 This explanation will account for the appearance of a notch in the figure at the point of 

 flexure of the embryo. The parallel neural ridges are shown in the anterior region, but 

 only the left ridge can (from this aspect) be traced round the bend and along the recurved 

 abdominal region ; the right neural ridge becomes quite concealed beyond the bend. Only the 

 appendages of the left side are indicated, although those of the right side showed through by 

 transparency. (See Fig. 7 in the text for illustration of the internal groove between the neural 

 ridges.) From specimen IV. 



Fig. 34. This is an exceptional embryo which in some respects is less advanced than 

 the preceding, and in other respects more advanced. Thus the antennae have not yet budded 

 out from the procephalic lobes and the lips have not commenced to enclose the manducatory 

 appendages, but the trophic vesicle has almost entirely disappeared from the region of the 

 trunk, and appears as a relatively enormous lobe springing from the head. Near the point 

 of abdominal flexure of the embryo there is still a trace of the posterior portion of the 

 trophic organ. The curious way in which this posterior remnant of the vesicle is bent up 

 is due to the fact that at that point the embryo was caught in a sharp bend of the uterus 

 like that shown in Fig. 32. 



In addition to the abdominal flexure there is the same caudal flexure which has been 

 noticed in previous embryos. Chorion omitted. From specimen III. 



Fig. 35. Stage X. In this stage the embryo has advanced considerably from the con- 

 dition observed in Stage IX. The caudal flexure has disappeared, or, in other words, the 

 tail has straightened out, and the point at which the abdominal flexure occurs has receded 

 backwards, so that the posterior end of the body now lies a long distance behind the head. 

 Meanwhile a cephalic flexure has occurred, so that the anterior end of the embryo is bent 

 backwards and does not point towards the vagina. The trophic vesicle is much reduced 

 relatively to the size of the embryo, but a long and very remarkable prolongation of the 

 vesicle extends beyond the head, covering over the ventral surface of the embryo. The first 

 appendage seen behind the antenna is the oral papilla. The embryo is shown removed from 

 the uterus, but enveloped by the chorion. From specimen IV. x 12. 



