ARTHROPOD A 269 



V. Gills. — Examine the gill-chamber, and the position of 

 the gills therein. Which appendages bear gills? How many 

 tufts to each appendage? How do they differ as to the place 

 of their attachment ? How many in all ? Make a table showing 

 these factors. 



VI. Internal Organs. — Remove with much care the carapace from the thorax 

 and the terga from the abdominal segments, by the use of scissors and forceps. 

 Sketch the organs in their natural position. What organs are visible? 



Examine in some detail the following sets of organs, 

 (a) The circulatory organs. (Use an injected specimen.) 



Heart: just beneath the carapace, in a membranous chamber (pericardial 



sinus). 

 Apertures, by which the blood enters the heart from the sinus; dorsal, 



ventral, lateral. How many do you find? 

 Arteries; anterior, posterior. 



(There should be, if possible, a permanent dissection of the lobster in which 

 the arterial circulation has been injected with a colored mass.) 



VII. Reproductive Organs. — These will be found immediately beneath the 

 pericardial sac as whitish (male), or yellowish to brown (female) lobed structures. 



Depending on the sex there will be found 



Ovaries or testes. Form, position, and number of lobes? 

 Oviducts or vasa deferentia. Course, length and outlets? 

 Can you determine the sex of your specimen? Note especially the external 

 differences between males and females. 



VIII. Digestive Organs. 



Liver, a pair of yellow, brown or reddish masses anterior to the reproductive 

 organs. 



Stomach; sketch in position. Dissect later, if time allows, and note the 

 anterior and posterior chambers, and the grinding apparatus. 



How is the mouth situated relatively to the stomach? 



Follow the intestine backward from the stomach to the 

 Anus: position of? 



Make a sketch of the entire tract from a side view, showing in what part of the 

 carapace each portion is. 



IX. Muscular System. — How is the abdomen flexed and how extended? How 

 do the muscle fibres run? To what attached? Are they plain or striate? How are 

 the appendages worked? Split open the segments of the cnela. 



X. Nervous System. — (If the time is short a demonstration may be made, 

 preferably with a lobster.) 



Remove the intestine, and cut carefully through the muscles in the median 

 line until the white ventral nerve-chain is uncovered. Follow it forward to the 

 head, cutting away the covering plates in the thorax. 



How many swellings (ganglia) in the abdominal region? Relation to the 

 segments? Where do nerves arise? 



Thoracic ganglia: number and relation to appendages? 



Sub-esophageal ganglion; circum-esophageal connective. 



Supra-esophageal ganglion (brain). 



