44 A MANUAL OF AMERICAN LAND SHELLS. 



descri])t.ions inider each species, but have not been able to reproduce 

 the figures, which, however, are referred to for examinatiou. 



I cannot too strongly urge upon my readers to examine the genital 

 system of each species. It is extremely easy, requiring nothing but a 

 shallow dish of water, over the bottom of which melted wax is poured, 

 to form a bed into which long ])ins are stuck as the organs are sepa- 

 rated by the pins, and a hand lens with a few needles stuck in handles 

 and a pair of small scissors. 



IV.— THE JAW AND LINGUAL MEMBEANE. 



As many of my readers are quite unfamiliar with this subject, espe- 

 cially most of those who have so largely contributed specimens for ex- 

 amination, I will describe in detail the position of the organs and the 

 ■method adopted for their study. 



On holding up against the light an individual of Meso<Jon thyroides in 

 one hand, and offering to him with the other some food (a piece of let- 

 tuce or carrot is always acceptable), one can readily see with the naked 

 eye the two organs here treated of. Above the external opening of 

 the mouth, through the transparent tissue of the head, is seen a small, 

 arched, reddish, free instrument, which appears to rise and fall as if 

 used in cutting off morsels of food. This is the jmv. 



On the floor of the mouth is the Ungual membrane, occupying about 

 the position of the human tongue. Its color is too nearly the same as 

 that of the head to aflbrd any strong contrast, but with close attention 

 it will be detected by its glistening silvery appearance, as it works 

 backward and forward. Its use seems to be to rasp the food and also 

 to force it back into the oesophagus. 



More detailed description, fully illustrated by figures, of the jposition 

 of these two organs, will be found in the chapters on Special. Anatomy 

 in Vol. I of Terr. Moll. U. S. 



On opening the head of Mesodon thyroides from above, one readily no- 

 tices at the extreme anterior part, close against the outer integument, 

 a prominent oval body.* This is called the buccal mass. It is easily 

 cut away from the animal, and will be found to contain both jaw and 

 lingual membrane. These can be removed by fine scissors or knives 

 from the buccal mass in the larger species, but in the smaller species 



*I must earnestly beg my readers to be deterred from this examination by no im- 

 aginary difficulties. It is the simplest and easiest process. Indeed, the same maybe 

 8ai<l of examination of the complete anatomy. All that is required is to carry it on 

 under water. The various organs are then readily separated. 



