THE PYCNOGOMDS. 45 



ganglia have completely telescoped, and this compound ganglia, 

 it will be remembered, innervates the second, third and fourth 

 pairs of appendages, as well as the proboscis. On the dorsal 

 surface (XX) is to be seen the two pairs of eyes equally dividing 

 the periphery of the cupola-like projection of the dorsal surface. 

 Sections do not give any additional facts worthy of note. 



The last stage of larval life, or rather the last stages showing 

 external traces of immaturity, is shown by Fig. XXI, stage 10, 

 and although after this the larva undoubtedly undergoes several 

 moults, accompanied by increase in size before becoming sexually 

 mature, it did not seem necessary to figure such intermediate 

 stages. The only change which has taken place in this stage 

 XXI is in the appearance of segmentation of the third pair of 

 appendages, and the number of the segments of this pair is that 

 of the adult. The second pair of appendages has also increased 

 in length, reaching to the distal end of the proboscis. All of the 

 walking legs have the adult number of segments. 



Having followed the larva through all these changes of growth, 

 it may not be out of place to say a few words about the adult 

 structures. A figure of the adult Tanystylum from the dorsal 

 surface is shown by Fig. XXII. The compactness of the body of 

 this species is exceptional and has been carried to such an extent 

 that the bases of the walking legs are almost in contact, so that 

 they radiate in all directions (except anteriorly) as from a cen- 

 tral point. In most other Pycnogonids there is not so great a 

 concentration of the body, and these undoubtedly come nearer to 

 the ancestral form, and, moreover, in some of these simpler forms 

 the rudimentary abdomen lies in the same plane as the body and 

 behind the attachment of the posterior pair of legs. The figure 

 for the anterior region of Phoxichilidium (Fig. XXI Y) shows a 

 form in which there is no such concentration. In Tanvstylum, 

 as seen in Fig. XXII, the abdomen has shifted far up on the back 

 of the animal, and is separated by only a short space from the base 

 of the prominence bearing the eyes. The adult still retains the 

 rudiments of the first pair of appendages. These have a large 

 basal segment and a smaller distal one covered with spines. 

 Both males and females develop the ovigerous legs, and the 

 males carry during the breeding season from one to three bunches 

 of eggs on each of these appendages, as shown in Fig. XXIII. 



