THE PULMONATA. 441 



Janellida?, the mantle is so much reduced that they are al- 

 most achlamydate. In the Snails, the mantle is large and is 

 produced into an asymmetrically coiled visceral sac, in which 

 the stomach, liver, and genital gland lie. The mantle-cavity 

 lies on the fore-part of the sac, and the anus opens on its 

 margin. Thus, in all the ordinary JPidmonata, the termina- 

 tion of the intestine is twisted from its normal position at the 

 hinder end, forward to the right dorsal, or haemal, aspect of 

 the body. 



When the pulmonary sac is posterior, and the pallial re- 

 gion small, the ventricle of the heart is anterior, and the 

 auricle posterior, and the animal may be said to be opistho- 

 pulmonate. On the other hand, when the pallial region is 

 large, and gives rise to a visceral sac, with the concomitant 

 forward position of the pulmonary chamber, the auricle is 

 inclined more or less forward and to the right side, and the 

 apex of the ventricle backward and to the left side. The 

 animal is thus more or less prosopulmonate. 



The mouth is commonly provided with a horny upper jaw, 

 as well as with a well-developed odontophore. Large salivary 

 glands are usually present. 



The heart consists of a single auricle and a single ventri- 

 cle. The aortic trunk, which proceeds from the apex of the 

 latter, divides into many branches, but the venous channels 

 are altogether lacunar. A renal organ lies close to the pul- 

 monary sac in the course of the current of the returning blood. 



There are usually two simple eyes, often lodged in the 

 summits of retractile tentacula. 



The Pulmonata are hermaphrodite. The generative gland 

 is an ovotestis, and is composed of branched tubuli, from the 

 cellular contents of which both ova and spermatozoa are de- 

 veloped (Fig. 123, III.). 



A narrow common duct leads from the ovotestis, and, soon 

 dilating, receives the viscid secretion of a large albumen- 

 gland. The much wider portion of the common duct beyond 

 the attachment of this gland is incompletely divided by longi- 

 tudinal infoldings into a sacculated, wider, and a straight, 

 narrower, division. The former conveys the ova, and the 

 latter the spermatozoa. At the end of this part of the ap- 

 paratus, the wider portion, which represents the oviduct, 

 passes into the vagina, which opens at the female genital 

 aperture, while the narrower portion of the common duct is 

 continued into a separate, narrow, vas deferens, the end of 

 which opens into a long invagination of the integument — the 



