T RAG HE AT A. 



317 



marked ganglia, and the nephridia (segmental organs 1 ), would render its 

 embryology of peculiar interest. Unfortunately Moseley was unable, 

 from want of material, to make so complete a study of its development 

 as of its anatomy. The youngest embryo observed was in part distinctly 

 segmented, and coiled up within the egg (fig. 168 A). The procephalic 

 lobes resemble those of the Arthropoda generally, and are unlike the 

 prse-oral lobe of Chastopods or Discophora. They are not marked off 

 by a transverse constriction from the succeeding segments. The three 

 embryonic layers are differentiated, and the interior is filled with a 

 brownish mass the remnant of the yolk which is probably enclosed 

 in a distinct intestinal wall, and is lobed in correspondence with the 

 segmentation of the body. The mouth invagination is not present, 

 and but two pairs of slight prominences mark the rudiments of the 

 two anterior post-oral appendages. 



The single pair of antennae is formed in the next stage, and is 

 followed by the remaining post-oral appendages, which arise in succes- 

 sion from before backwards somewhat later than the segments to 

 which they appertain. 



The posterior part of the embryo becomes 

 uncoiled, and the whole embryo bent double 

 in the egg (fig. 168 B). 



The mouth appears as a slit-like opening 

 between and below the procephalic lobes. On 

 each side and somewhat behind it there grows 

 out an appendage the first post-oral pair (fig. 

 Ig9 ? l) while in front and behind it are 

 formed the upper and lower lips. These two 

 appendages next turn inwards towards the 

 mouth, and their bases become gradually closed 

 over by two processes of the procephalic re- 

 gion (fig. 170, m). The whole of these struc- 

 tures assist in forming a kind of secondary 

 mouth cavity, which is at a later period fur- 

 ther completed by the processes of the pro- 

 cephalic region meeting above the mouth, 

 covering over the labrum, and growing back- 

 wards to near the origin of the second pair of 

 post- oral appendages. 



The antennae early become jointed, and 

 fresh ioints continue to be added throughout 



, ' . ,. ,1 l 1, ,1 OF .fERlPATUM UA.rii.Hoin, 



embryonic life ; in the adult there are pre- slightly older than A in 



sent fully thirty joints. It appears to me fig. 168; unrolled. (After 



probable (though Mr Moseley takes the con- Mo f^ tenn{E; . mouth; 



trary view) from the late development 01 / intestine; c. procephalic 



the paired processes of the procephalic lobes, lobe, l, 2, 3, etc. , postural 



which give rise to the circular lip of the appendages. 



1 F. M. Balfour, "On certain points in the Anatomy of Peripatus capensis." Quart. 

 Journ. of Micros. Science, Vol. xix. 1879. 



Fin. 169. 

 PERIPATUS 



EMBRYO 



