XUDIB RANCH MOLL UXK*. 



205 



The Nudibranch mollusks, such as the Eolis and Doris and 

 allied forms, breathe by external gills, arranged in bunches 

 on the back, as seen in Fig. 195, jflolis (Mon- 

 tagua) pilata (Gould), a common species on 

 the coast of New England. In Doris (Fig. 

 197), they are confined to a circle of pinnate 

 on the hinder part of the back. They are 



FIG. 195. 



FIG. 196. 



FIG. 197. 



Fig. 195. >"ofe,aNudihranch. 



Fig. 190. Veliger of Tergipes. v, velum ; s, shell ; d, foot ; o, otocysts. Alter 

 Schultze. 

 Fig. 197. Doris bUamellala. New England coast. 



shelless, and not uncommon just below low-water mark, 

 laying their eggs in jelly-like masses coiled up on stones and 

 the surface of sea-weeds. Though the adults are shelless, 

 the embryos at first have a shell 

 (Fig. 196, s), indicating that 

 the Nudibranchs have descend- 

 ed from shelled Gastropods. 



Fig. 196 represents the veli- mg , m ._.p fl y 8a M er oBtropha. Com- 

 ger Of Tergipes ladnulata mon pond-snail. After Morse. 



Schultze, allied to Doris, with its large ciliated velum, and 

 protected by a deciduous shell, which finally disappears with 

 the velum. 



The air-breathing mollusks, Pulmonata, are represented by 

 the pond-snails, Pliysa (Fig. 198) and Limnams (Figs. 199, 

 200), and the land-snails and slugs. Fig. 205 represents a 

 slug suspended by a mucous thread from a twig. 



The common snail, Helix albolabris Say, is a type of the 

 air-breathing mollusks. Fig. 201 represents this snail of 

 natural size, in its shell. The opening to the lung is seen 

 at a, and at B is represented the heart and lung of the gar- 

 den slug (Liinii.f flavus). Fig. 202 represents Helix albo- 

 labris with the shell removed, and the mantle thrown back. 



