THE RELATIONSHIPS OF THE SEA-SPIDERS. l6l 



larval forms themselves to have been inter-related at 

 the time when they diverged into Sea-spiders, Annelids, 

 and Crustacea. My own view of the question is that we 

 have here a condition represented by Fig. 4, B, or, in 

 other words, that the Pantopod-larva represents purely 

 a secondary larval form. 



I wish now to bring forward the reasons which have 

 led me to such a belief, and at the same time the objec- 

 tions to the views of Dohrn and Hoek. 



Let us stop for a moment and examine the structures 

 of the three larval forms under discussion. 



NAVPLIJJS 



The Nauplius of the Crustacea is shown in Fig. 5. 

 The body is oval in outline, and unsegmented ; it has 

 three pairs of appendages arranged along the sides of the 

 body. The mouth lies under a large upper-lip, a little 

 anterior to the centre of the body, and leads into the 

 oesophagus which in turn opens into the stomach or 

 mid-gut ; then follows the proctodseum with its exter- 



