232 SYNOPTIC COLLECTION. 



black eyes are distinctly seen at the ends of the longer 

 pair. No. 507 is a model showing the internal organs of 

 Helix pomatia Linn. The various parts are marked ; 

 those on the left are the buccal body, esophagus, salivary 

 glands, stomach, liver, intestine, and the pulmonary cham- 

 ber ; and those on the right the reproductive organs and 

 slime glands. 



The land Gastropods most specialized by reduction are 

 the slugs, represented by Limax (Nos. 508-511). Here 

 the shell is reduced to a thin, flat plate on the back (see 

 model of Limax maximus Linn., No. 508), and this has 

 become internal. The spiral body of most Gastropods 

 no longer exists, but the body of the slug is long with the 

 foot on the ventral side (No. 509, L. flavis Linn.). The 

 preparation (No. 510) shows the general anatomy of 

 Limax rufus, while the genital organs are seen in No. 



5"- 



Section 9 of Case B is taken up with the Tectibranchs, 



Nudibranchs, Scaphopoda, Heteropoda, and Pteropoda. 

 These are considered as so many groups of molluscs which 

 have become modified, each in its own special and dis- 

 tinctive way, to meet the requirements of existence. The 

 Pteropods are probably the most specialized, and the most 

 closely related to the Cephalopods; but on account of 

 their minute size, they are placed in the horizontal part 

 of Section 9. Here they can be seen and studied more 

 easily than in the erect portion, where, according to our 

 system, they properly belong. 



Some of the Tectibranchs have well developed shells, 

 like Tornatella (No. 512, T. solidula Lam.) and Bullus 

 (No. 513, B. oblongus A. Adams), while in others 

 (Aplysia, No. 514, see erect part of Section, No. 515, and 

 Pleurobranchus, No. 516) the shell exists only as a vestige. 

 Tornatella (No. 512), reminds one of Oliva (No. 482) with 

 its short spire and large body whorl. Bullus (No. 513) 

 even when young shows no spiral form, but if a cross 

 section of the shell is made near the posterior end the 



