THE PYCNOGONIDS. 43 



were interpolated at similar places to those of the preceding leg, 

 viz. in the middle of the fourth and in between the fifth and 

 sixth. There is an undeveloped pair of appendages at the pos- 

 terior part of the larva, and the abdominal part of the body, 

 instead of lying between them, as previously, has now moved 

 dorsalwards, so that it projects from the posterior-dorsal part of 

 the embryo. The first and second pairs of ventral ganglia (the 

 first and second and the third in a true count) are in close con- 

 tact or partially fused. The reproductive organ has much 

 increased in size. In the region of the first pair of walking legs 

 it extends through a few sections as two entirely separated parts, 

 lying on each side of the middle line. In the region of the 

 second pair of walking legs the two lateral parts unite into a 

 single median structure which is almost as broad as the body, 

 and the organ ends soon after this as a median, thickening on 

 the mid-dorsal surface of the digestive tract. The glands of the 

 mandibles have almost entirely disappeared. 



At the next stage of development we have the formation of 

 the seventh and last pair of appendages {stage 8), Fig. XVIII. 

 There is a great increase in size, and an important change takes 

 place in the second appendage. These lose their early larval 

 structure and probably their first function, and now enter 

 upon a new role. They are three-jointed and have lost the large 

 terminal spine. The tip of the appendages is covered with many 

 smaller spines, and sometimes I have seen one larger than the 

 others, which presumably represents the large terminal claw of 

 the preceding stage. The appendage is now three-jointed, having 

 acquired an additional segment. 



The first pair of appendages do not differ from the preceding 

 stages. The third pair is. still in an undeveloped condition, 

 although somewhat larger than in the last stage. The fourth 

 and fifth and sixth pairs have each eight segments, but the 

 seventh pair, which has just been acquired, has only six segments. 

 All of the walking legs have increased greatly in length, and 

 each contains a long diverticulum from the digestive tract. Five 

 pairs of ventral ganglia are seen, although the first and second 

 are almost completely fused. 



Sections show that the mid-gut sends out diverticula to the 

 first, fourth, fifth, sixth, and seventh pairs of appendages and a 



