10G Tlie Lungs, Heart, and Blood-vessels of the Slug. 



old structures, and carries it away to tlio various sewers 

 (glands, etc.), of which the lung is one. 



This refuse or effete material is of many sorts, each of which 

 is removed by a separate channel, thus : — Urea is got rid of 

 through the kidneys, bile through the liver,* and lactic acid 

 through the skin. In the lung, the foul air (carbonic acid) is 

 discharged, the oxygen of the fresh air is taken in, and the 

 blood is altered in properties and constitution. 



Having your slug fixed in the way described in a former 

 number,f seek the pulmonary opening. This is placed on 

 the right side, in the middle lateral line, and at about half 

 an inch from the right upper tentacle. It is of an elliptical, or 

 rather of a double wedge-shaped outline, and may readily be 

 distinguished whilst the animal is breathing, owing to its snow- 

 white lining, which is now and then everted, contrasting 

 markedly with the dark black hue of the outer skin. Before 

 you begin your dissection, it will be as well to map out dis- 

 tinctly the extent of the lungs, which may easily be done as 

 follows ; — Take a thin glass tube, slightly drawn out at one 

 end, and insert it into the orifice, which, with a little care, you 

 may easily do ; then blow the air somewhat forcibly from your 

 mouth, and the lungs of both sides will become visibly inflated, 

 together with the passages of intercommunication, in this man- 

 ner indicating with clearness the exact limits of the pulmonary 

 system. 



Having formed a general notion of the whereabouts of the 

 lung sacs, next place the point of your curved knife within 

 the orifice, and keeping the blade as horizontal as possible, cut 

 steadily backwards, and in a line parallel with the middle lateral 

 plane till you reach the membranous constriction which sepa- 

 rates the thorax from the abdomen ; at this partition the lung 

 ends posteriorly. As yet you have only exposed the right lung, 

 but since it communicates with its fellow of the opposite side 

 throng]] two distinct channels, by laying them bare, you may 

 then come upon the left sac. 



Place your long-bladed scissors in the hinder passage 

 (which lies quito in front of the constriction referred to, and in 

 the transverse plane), and with the blades as close to the parti- 

 tion as possible, cut from right to left through the integument. 

 You now reach I he left lung sac, but before you can examine 

 it yon must make two other incisions. 



1st. Cuf from behind forwards, parallel to your first incision, 

 till you arrive at (he anterior end of tho sac. 



* Tho Lilo is not entirely worn-out mailer, for although if retained in the 

 system (of man), it tingei the skin and poisons tho brain, producing jaundice, it is 

 in some unknown manner rabsan Lent to the enda of digestion. 



t Fide IXTSLLXOTUAIi Omsbtbb, for May, 18G3. 



