Introduction to A nimal Morphology. 211 



neural flexure, except, perhaps, in Limacina. The 

 anus is mostly lateral, near the front edge of the 

 mantle, or in shell-less forms under the fin. The 

 salivary glands are tubular caeca in Clione and Pneu- 

 modermon, rudimental or absent in others. The liver 

 is large and lobed in Thecosomata, or as numerous 

 yellow or green gastric caeca in Gymnosomata. These 

 organs lie in a single or partly divided sac. 



The heart, which is not rhythmic in action, lies in 

 front of the visceral sac (Cymbulia), to its right (Pneu- 

 modermon), to its left (Limacina), or within it, and con- 

 sists of an auricle with thin walls of branched muscular 

 fibres, ciliated within, and a globular or pear-shaped 

 ventricle of thick, transverse muscle, non-ciliated, 

 having a double auricular, and one (Hyalea), two 

 (Styliola), or no (Cleodora) aortic valve. The aorta 

 sometimes begins in a bulb, and gives an anterior 

 cephalic branch, traversing the nervous collar to the 

 epipodia, and a posterior, visceral. The heart is in a 

 thin-walled pericardium in Hyalea, Pneumodermon, 

 &:c. The arteries are thin-walled, and end in lacunae, 

 as there are no capillaries nor veins, unless the 

 channel from the front of the kidney to the gill-shield 

 in Styliola be considered as a vein. From the lacunae 

 the blood enters the auricle. The gills may be two, 

 absent (Pelagia), or crescentic lateral folds in the 

 mantle cavity (Hyalea), or a ciliated shield on the 

 ventral side of that cavity (Styliola), or the lining of 

 the whole or part (Limacina) of the mantle-sac, or ex- 

 ternal leaf-like appendages (Pneumodermon), or an 

 outer terminal ring (Spongobranchia), or a median 

 ciliary girdle (Trochocyclus). The excretory organ 

 (kidney) is tubular, with one opening within the 



