48 T. H. MORGAN. 



parent. This larval form shows certain differences from that of 

 Tanystylum. In it the second and third pairs of legs are much 

 longer, as the distal spine is prolonged out into a long thread- 

 like continuation of the limb. In Tanystylum these spines were 

 thick and short and adapted for crawling amongst the hydroids, 

 while the long limbs of the larva of Phoxichilidium could hardly 

 be used in this way, and suggest rather that they are used for 

 catching to any objects they may come in contact with. The 

 first pair of appendages are thicker in Phoxichilidium, with 

 smaller claws, and the proboscis, instead of projecting forward 

 between the first appendages, is only raised slightly above the 

 level of the body at about its middle point. I have not 

 obtained later stages of this larva, but the accounts of other 

 species of this genus show that it becomes parasitic either inside 

 the digestive tract of a hydroid or buried in its substance, and 

 here it undergoes its metamorphosis until the adult structures 

 are almost reached. 



The other figure (XXYI) is of a young Pallene after it has 

 left the parent, and this individual was found living freely 

 amongst the Pennaria. The figure shows a ventral view, and 

 the stage corresponds to one following that shown by Figs. VII 

 and VIII of Plate IV. It shows the third pair of appendages 

 beginning to develop, which, in Figs. YII and VIII of Plate 

 IV, only appeared as two slight projections from the sides of 

 the body. In the present case these appendages are folded 

 across the breast — if the term be applicable to Pycnogonids — 

 closely adhering to it in the region between the base of the pro- 

 boscis and the first pair of walking legs. The embryo has also 

 fully developed its fourth pair of walking legs, which, it will be 

 remembered, were in an undeveloped state in the previous stage.] 



