EXPLANATION OF PLATE X. 



Creseis acicula. 



Fig. 1. Cresei* cicala. Several of the internal organs are drawn 

 in optical section, a. anus ; al. gl. receptaculum seminis : 

 c. f. ciliated furrow for conveying spermatozoa from the 

 sexual orifice to the penis ; ci. sh. ciliated shield, respira- 

 tory in function ; /. n. main branch of fin-nerve ; f/.'sub- 

 oesophageal portion of central nerve mass, showing the 

 great fin-nerves being given off from the anterior corners, 

 and the otoconia lying beneath ; h. d. duct of receptaculum 

 seminis ; h. yl. ovo-testis, or hermaphrodite gland ; 

 i. intestine ; 1. liver ; in. I. middle and rudimentary lobe 

 of foot ; in. n. mantle nerve ; up. nephridium : o. mouth ; 

 oe. oesophagus ; ot. one of the two otocysts, containing, 

 not a single spherical body or otolith, but numerous small 

 calcareous bodies, whose mass is termed an otoconia, 

 (the function of these bodies is supposed to be auditory) : 

 p. o. penial aperture situated at the base of the rudimen- 

 tary right tentacle; p. cj. penial gland, or rather, the 

 indrawn penis ; r. m. retractor muscle ; sit. shell ; st. 

 stomach : siv. I. swimming lobe or fin ; ut. di. uterine 

 dilatation ; ve. ventricle of heart. 



Fig. 2. View of an entire Creseis (Fig. 1. had to be drawn in two 

 portions, as the length was too great for the size of the 

 plate). 



Fig. C shows the homologies of a typical Pteropod larva, (Cymlulia), 

 with the larvae of typical Gastropods, A and B ; A being 

 a younger and B an older stage. (After Gegenbauer). 

 v. velum ; c. shell ; /. foot ; op. operculum : t. tentacles. 



Fig. D. Diagram of a simple bilaterally symmetric or Isopleurous 

 Gastropod (Chiton). 



Fig. E. Diagram of an asymmetric or Anisopleurous Gastropod. 



Fig. F. Diagram of a naked Pteropod. 



Fig. G. " thecate or shell-bearing Pteropod. 



Fig. H. " Cephalopod. 



(All after Lankester, G being modified). 

 D, V, A, and P point respectively to the dorsal, ventral, anterior 



and posterior aspects of the body. 



The extent of the foot in each case is denoted by the dntted 



shading. 



o. mouth ; a. anus ; ff. fore-foot ; in. f. mid-foot : h. f. hind-foot : 



ep. epilobium ; c. e. cephalic eyes : s. p. sub-pallial space : in. s. mantle 



skirt or flap : ?'-s. visceral hump or dome. 



(The original figures copyrighted, March, 1895). 



