THE PYCNOGONIDS. 39 



internal organs could be made out from the surface, so that sec- 

 tions were again resorted to. Here it was found that the mid- 

 gut gave off the usual diverticula to the first and third pairs of 

 appendages and, besides, quite a large pair of pouches into the 

 undeveloped fourth pair of appendages. The sections show that 

 the gut ends blindly behind, and no trace of proctodeum was 

 found. The lumen of the digestive tract is almost entirely 

 obliterated by the large size of the cells, and these are completely 

 filled with spherules of yolk. Large, active ectoblast and meso- 

 blast cells, together with the mid-gut, fill up the posterior part 

 of the embryo. The fourth pair of appendages is quite far 

 advanced, as the ectoblast, by pushing in from behind, has par- 

 titioned off on each side a part of the posterior part of the body. 

 The ingrowth of ectoderm on each side is always two-layered, fur- 

 nishing a new wall to the outer sides of the body and to the 

 inner side of each new leg. The first (double) pair of ventral 

 ganglia is followed by a well-developed second pair, each con- 

 taining large cavities, and these are followed by a smaller fourth 

 pair of ganglia. There is a single pair of eyes. 



The next embryo which I have found shows a considerable 

 increase in size, and I cannot be certain that it is the stage fol- 

 lowing the last. Still it is probable, as I have found five or six 

 of this size and none in between this and the last. The larva is 

 shown by Figs. XIII and XIY giving the ventral and dorsal 

 views of this stage (4th). The most marked external change is 

 in the great elongation of the body posterior to the third pair 

 of appendages, and in this region we can distinguish a central 

 middle lobe and a pair of lobes on either side of this closely 

 pressed against the middle part, the side lobes being the ' anlage' 

 of the fourth pair of appendages. Three pairs of ventral ganglia 

 were made out from surface views, but sections show also a small 

 forming fourth pair. The embryo shown by Fig. XIV is the 

 same, but from dorsal view. It shows a slight constriction in 

 the middle of the body at the base of the fourth pair of append- 

 ages, and the continuation of the body posteriorly between these 

 appendages is seen to be broader than the same region on the 

 ventral surface; and further the base of the middle posterior 

 lobe suddenly widens out, as seen in the figure. A single pair 

 of eyes is shown on the anterior dorsal surface. Sections of this 



