2. Blood vessels cut across and tilled with coagulated blood. 



3. Mesenteries or dorsal and ventral membranes connecting the 

 digestive tract with the body wall on the median line. 



4. Septa and nephridia cut at various angles. 



Make drawings to show the histology of the nervous system and 

 bod\ cavity. 



XI. CAMBARUS SP. (The Crayfish). 



A. GENERAL CHARACTERS. 



I. BODY. 



Note that the animal has a body proper and a series of paired 

 appendages. The body is bilaterally symmetrical and divided into 

 a posterior jointed abdomen and an anterior portion the ccphalo- 

 thora.r. The entire body is covered by a hard calcarious shell the 

 e.roskeleton which is flexible at the joints where movement may take 

 place. 



II. APPENDAGES. 



Note that all of the appendages are jointed, that they are attached 

 in pairs to the ventral surface of the body and that they vary much 

 in size and form. 



Make a drawing of the crayfish as seen from the dorsal side. 



III. APERTURES. 



Make out the following apertures in the body wall: 



1. The mouth seen under the anterior part of the cephalothorax 

 after separating from one another the crowded appendages. 



2. Anus, a much elongated slit upon the lower side of the ter- 

 minal piece of the abdomen, the telson. 



3. Genital openings on the basal joints of the legs: (a) In the 

 male on the delicate papilla on the last appendage of the cephalo- 

 thorax (one on the right and one on the left ) ; (b ) in the female an 

 opening with a valve-like edge on the antepenultimate appendage of 

 the cephalothorax (one on the right and one on the left). 



4. Auditory organs : A small opening on the appendage (anten- 

 nule ) just under each eye stalk. 



5. Green glands : A large opening on the first joint of the next 

 following appendage (antenna) on each side. 



B. ABDOMEN. 



This is made up of six segments or somites bearing appendages 

 and a terminal, seventh piece, the telson, which is subdivided 



45 



