EXPLANATION OF PLATE IV. 



Fig. 1. Adult worm (Polydora) enlarged under a lens. 



„ 2. Great hooks of the fifth segment of the body ; a, as usually seen 

 in the separated and perfect organ under pressure; 6, more 

 complete as obtained in the living animal or in a favourable 

 spirit preparation x 700 diameters. 



„ 3. Spear-tipped bristles accompanying the former x 700 diameters. 



,, 4. Hooks of the posterior region of the body ; a, pressed between 

 two glasses ; b, seen in front, so as to exhibit both wings, x 700 

 diameters. 



„ 0. Front and side view of two of the Vjristles of the same species, 

 X 700 diameters. 



„ 6. Caudal segment and its cup, x 210 diameters. The whole of th« 

 figures and explanations after Prof. W. C. Mcintosh. 



