112 GENERAL BIOLOGY 



resemblance to the third abdominal? Are protopodite, 

 exopodite and endopodite present? 



Draw the first, the third and the last walking appendages. 

 The first pair are called chelae. 



Remove the mouth parts on the same side, and arrange 

 them in order. From the outside inward they are called: 

 3d pair of maxillipeds, 2d pair of maxillipeds, 1st pair of 

 maxillipeds, 2d pair of maxillae, 1st pair of maxillae, mandibles. 

 Compare each one of these with the third abdominal ap- 

 pendage and with the walking appendages. Are they bira- 

 mous, are the protopodite, the exopodite, and the endopodite 

 present? Are the appendages of this group alike? Might 

 they be considered as modifications of a common structure? 

 Do they have the same number of joints as the walking 

 appendages? In the 2d maxilla note the gill bailer which 

 lies in the gill chamber and whose movement creates a 

 current of water which passes over the gills. 



Draw the 3d maxilliped, the 2d maxilla, and the mandible. 



Remove the antenna and the antennule from the same 

 side of the body. Compare with the other appendages, 

 what are the likenesses and the differences? Draw. 



Considering all the appendages, indicate whether there 

 is a common plan in their structure, and if so what it is. 

 Also indicate what the departures from this plan have been, 

 and suggest advantages of these variations. Parts having 

 the same fundamental structure are said to be homologous; 

 and in this animal there is represented a serial homology. 



HE. Internal Anatomy. 



1. Respiratory System. Carefully cut away the carapace 

 from the side of the body and expose the gill chamber and 

 the gills contained therein. What is the form of the gills? 



