74 LABORATORY DIRECTIONS 



17. The first pair of feelers, the antennules, though two 

 branched are not 'biramous.' Their location upon the prostomium, 

 which is not a true segment, their development, and their 

 structure all indicate that they are not homologous with the other 

 appendages. Note that three segments are interposed between 

 the body and the two branches or flagella of each antennule, 

 while but two segments are found in the protopodite of a true 

 biramous appendage. 



1 8. While the walking legs of the crawfish are not biram- 

 ous in any stage of their development there are indications that 

 they are biramous appendages which have lost the expedite. The 

 crawfish is a near relative of the lobster but the development of 

 the crawfish has been greatly shortened so that the young when 

 hatched from the egg resembles the- parent. On the other hand 

 the lobster passes through a distinct series of free-living larval 

 stages before acquiring the general body form of the adult. In 

 these larval stages of the lobster the walking legs are typical 

 biramous appendages made up of protopodite, expedite, and end- 

 opodite. During later development the exopodite disappears, leav- 

 ing only protopodite and endopodite for each walking leg. These 

 same parts are recognized in the walking legs of the crawfish. 



Remove the walking legs and study to secure data for com- 

 pleting the table but no drawings are required. 



19. The genital openings of the male occur on the basal 

 segment of the fifth pair of walking legs, while those of the fe- 

 male occur in a similar position on the third pair of walking legs. 

 Note that the first two pairs of abdominal appendages are dif- 

 ferent in the two sexes. Examine both sexes but no drawings 

 are required. 



20. In the male the first two pairs of abdominal appendages 

 are highly modified for use in copulation and are not easily hom- 

 ologized. When at rest they lie in a groove directed forward be- 

 tween the bases of the walking legs. In the female the first pair 

 of abdominal appendages is also modified. In the table asked for 

 under section 9 do not try to work out the homologies for these 

 modified structures of the first two or first abdominal appendages. 



