Tlie Lobster. 83 



and mandibular. We know that in front of the groove 

 three segments are represented, because related Crusta- 

 ceans (Squilla, Eupagurus, Gebia, Callianassa) show these 

 three segments more or less free, and in the lobster there 

 are three pairs of appendages. It is probable that in the 

 lobster the terga were also once free though now consolidated. 



Elevate the free edges of the carapace and give reasons, 

 if you have any, for considering them homologous with the 

 pleura. Note the marginal hairs. Where are they most 

 abundant ? Their function ? W T ith a strong knife cut away 

 all the right side which lies posterior and ventral to the 

 groove. Note that the inner layer is membranous. Is it 

 continuous at the margin with the outer layer? How far 

 dorsally does the membranous part extend? Follow the 

 line of its union with the epimera. 



The space between the pleural piece and the epimera is 

 the gill or branchial chamber. How many gills are there 

 arising from the thoracic protopodites ? Carefully remove 

 these podobranchice with their associated flabella, keeping a 

 record of their position. Above each exposed protopodite 

 is a membranous interarticular membrane which bears the 

 arthrobranchicE. Record the number and position of the 

 arthrobranchiae. Above, are the four pleurobranchice. They 

 belong to which segments ? 



Granting that the transverse groove marks the dividing line 

 between two segments, it is reasonable to suppose that the 

 part lying immediately behind it must represent a portion of 

 the tergum and pleura of the mandibular segment. The 

 fused thoracic epimera now being exposed, it is clear that 

 the posterior portion of the carapace is certainly independent 

 of the six posterior thoracic rings. To just which of the 

 remaining segments, mandibular, maxillary or maxillipedal, 



