IX 



FRESH-WATER MUSSEL. 



Dissection. Cut through adductor muscles of one side and remove the valve. Note the beating of the 

 heart. Kill with hot water. Harden in spirit before following the course of the alimentary canaL 



LOBSTER OR CRAYFISH. 



Dissection. Eemove lateral portion of carapace by passing a knife under its free edge from the posterior 

 end to cervical suture. This part of the carapace is the gill-cover or branchio'stegite (Gr. steyo, I cover). 

 Notice scaphognathite working. Turn out the gills with the knife. Dissect from the left side, as in PL XIII. 

 figs. 2 and 3. 



Place another specimen under water in dissecting dish and it soon dies. Remove dorsal portion of 

 carapace and of abdominal somites with scissors, in order to make out the chief organs, as in PI. XIII. fig. 1. 



Preparation of Skeleton. Boil in strong potash solution, which dissolves everything but the chitin or 

 horny substance composing the shell The parts of the exoskeletou may be disarticulated and laid out in their 

 natural order. 



SNAIL. 



The Edible Snail is the largest of all the Snails, hence its convenience for study ; but the Common Snail 

 may be taken. Snails can be kept alive for a considerable time, and warm water generally makes them 

 protrude from their shell. Boiling water kills them. 



Dissection. Remove shell bit by bit with strong forceps, and pin the animal out in spirit, dissecting from 

 the dorsal surface. Lay open pulmonary chamber, then expose the viscera by laying open the dorsal integu- 

 ment of foot along middle line and removing the mantle. The viscera may next be laid out to display them to 

 advantage. 



FROG. 



The Edible Frog is chosen on account of its larger size, but the Common Frog will also show the 

 various points. Kill with chloroform. 



Dissection. A dissection from the ventral surface may be made under water in the dissecting dish by 

 cutting through the skin in the middle line from the symphysis of lower jaw to symphysis of pubis ; then pin 

 out the skin on both sides, and various muscles, veins, etc., are brought into view. Next open abdomen a little 

 to one side of anterior abdominal vein, cut through shoulder-girdle, and remove its central portion. The 

 various viscera are then seen as in PI. XVIII. fig. 2. 



Turn over viscera to right side, cut away parts mentioned in PI. XVIII. fig. 3 (text), and pin out with left 

 side upwards so as to get the sectional view. 



Prepare a specimen in spirit and nitric acid for the dissection of the nervous system. Dissect from dorsal 

 surface, and remove the dorsal wall of the cerebro-spinal cavity by nipping it away with scissors, beginning 

 at the junction of the skull and spinal column. Dissect out cranial nerves and the nerves of the limbs for 

 a short distance. Remove brain and spinal cord and preserve in spirit for future use. 



Take a similarly prepared specimen and dissect from ventral surface. Remove the bodies of the vertebrae 

 and the floor of the skull. Along each side of the spinal column dissect out the sympathetic system, and trace 

 its connection with the cranial and spinal nerves as in PL XX. diag. 1. 



The principal cranial nerves may be dissected from the left side, as in PL XXI. fig. 5, after distending the 

 gullet with a piece of glass tubing. Place in chromic acid, with a little nitric acid to hasten the softening of 

 the bone and the hardening of the nerves. 



Section of Spinal OorJ. Take a piece hardened in spirit, prepare and imbed in paraffin aa before, and 

 mount transverse sections in glycerine. 



Circulation in Web. In a thin piece of wood or cork make a notch to fit the web between two of the toes. 

 Stretch the web over the notch by thread attached to the ends of the two toes. Keep the skin moist with wet 

 blotting-paper, and after placing a small drop of water on the web, cover with triangular cover-glass for exam- 

 ination under high power. 



Preparation of Skeleton. After cleaning the bones roughly, steep for about a week in sufficient water to 

 cover them, then place them for a few days in fresh water, which should be frequently renewed. They may be 

 cleaned with a brush and then laid out in the sun to bleach. Any grease may be extracted from the bones by 

 benzol 



