LIMULUS 191 



7. At the base of the caudal spine notice the anus. 



Make a drawing of the ventral surface. 



Internal Anatomy. — If the Limulus is alive the simplest 

 method of killing it in preparation for dissection is to cut 

 off the legs and allow the blood to drain off from the large 

 blood sinuses which extend into each leg. 



In order best to remove the heavy carapace it is desir- 

 able to make several cuts in the exoskeleton with a hacksaw 

 or a fine-toothed saw. (For an outline showing a good 

 method of making the cuts, see Cole.) With cuts properly 

 made lift a corner of the carapace slightly, and with scalpel 

 cut away the adhering tissue. Use short cuts and keep the 

 cutting edge close to the inner surface of the exoskeleton. 

 With the carapace raised in the region of the compound 

 eyes it is possible to see the nerves leading to these organs. 

 When the piece of the cephalothoracic exoskeleton has been 

 cut free from adhering tissue, the ligament along its pos- 

 terior border should be cut and the entire piece removed. In 

 cutting these ligaments be careful not to cut too deep for 

 the heart lies close to the surface at this point. It is best 

 to remove the abdominal exoskeleton by beginning at the 

 posterior end. Cut the inter articular membranes at the base 

 of the telson and lift the abdominal carapace slightly. The 

 two rows of depressions seen on the surface of the latter in- 

 dicate the position of chitinous infoldings of the exoskeleton, 

 called entapophyses. The heart lies, in large part, between 

 these rows. Slip the scalpel (or a small pair of bone 

 forceps) under the exoskeleton and cut the entapophyses one 

 at a time. The exoskeleton may now be separated from the 

 soft tissues underneath and removed. The animal should 

 now be placed in a large crystallization dish and the rest of 

 the dissection carried out under sea water. 



The Circulatory System. — Remove such portions of the 

 gonads (orange masses) and liver tissue (yellow masses) as 

 may cover the heart and major blood vessels. The heart 

 will now be seen as a long tubular organ lying enclosed in 



