370 PULMONEA; SLUGS. 



VII. SCUTIBRANCHIATA. In these, also, there la a consider- 

 able resemblance to the Pectinibranchiata in the form and 

 position of the gills ; but the shells are very open, scarcely in 

 any degree spiral, and cover the body and gills like a shield ; 

 and they also differ essentially in their mode of reproduction. 



VIII. CYCLOBRANCHIATA. These Mollusks have their gills 

 disposed in little tufts under the margins of the mantle, much as 

 in the Inferobranchiata ; but they have shells, which are spread 

 out over the body, and differ from that Order in their mode of 

 reproduction. 



ORDER I. PULMONEA. 



912. Although the greater part of the Mollusks of this 

 Order live on land, some are aquatic ; but these, like the aquatic 



FIG. 562. LIMAX 



air-breathing Insects and Vertebrate, are obliged to come occa- 

 sionally to the surface to breathe. They all feed upon vegetables, 

 and many of them do so exclusively ; but some are extremely 

 voracious, and will devour almost any organised matter that 

 falls in their way. They are diffused through all climates, 

 particular species being restricted to eaeh. Those without a 

 shell, commonly known as slugs, constitute the family LIMA- 

 CINJE. In the common Slugs^ as in most of the terrestrial species 

 of this Order, we observe a prominent head, with four tentacula ; 

 and at the end of the longer pair the eyes are situated. These 

 tentacula can be drawn inwards, by a process resembling the 

 inversion of the finger of a glove. On the back there is a kind 

 of shield or disk, formed by the mantle, which sometimes incloses 

 a small shell. This shield covers the pulmonary sac, the opening 

 of which is on its right side, and the head can be withdrawn 



