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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVIII. 



ing disk. But by far the larger portion of these thorax muscles are 

 the powerful locomotor agents which operate the second (h) and third 

 (i) swimming legs and make of them the chief propelling organs. 



Each of the appendages and the mouth tube are also plentifully sup- 

 plied with muscles, both flexors and extensors, and a good idea of the 

 service performed by each may be obtained from an examination of its 

 muscle supply. The anterior antenna? have two extensors and one 

 flexor. The powerful muscles used in the second antenna? for clasp- 

 ing are quite similar to those in the second maxillipeds (fig. 26) and 

 nearly fill the basal joint. 



Thejr are much larger and stronger in the male than in the female. 

 We have alread}^ seen that the appendages themselves are larger in the 

 male and form the chief organs for clasping. 



There are four short and narrow muscles attached to the base of the 

 proboscis framework by means of which the 

 latter may be elevated to a right angle with 

 the ventral surface (j). Other muscles extend 

 posteriorly and laterally and assist in the ele- 

 vation or depression of the tube when suck- 

 ing up food (k). 



The muscles controlling the mandibles are 

 surprisingly large and strong and fairly prove 

 that these appendages are vigorousty used in 

 the process of eating, which is hardly con- 

 ceivable if the creature feeds on mucus. 

 They extend outward and backward obliquely 

 to the very margin of the carapace about 

 opposite the first pair of legs (1). 



In the female the muscles of the first max- 

 illa? are as small and degenerate as the maxilla? 

 themselves; but in the male they are much 

 better developed and must give these append- 

 ages a strong clasping power. The muscles of the second maxilla? are 

 better developed than those of the first, and they are larger and stronger 

 in such genera {L&peophthevrus, etc.) as have these appendages bifur- 

 cate (m). 



The muscles of the first maxillipeds are veiy meager in both quantity 

 and quality, and, with the weak structure of the appendages, show 

 plainly that the} r are not of much service to the animal. And Picker- 

 ing and Dana are probably right when they bestow upon them the 

 appellation '"rudimentary." A good idea of the musculature of the 

 second maxillipeds can be obtained from fig. 26. These are the prin- 

 cipal clasping organs, and the muscles which operate them are both 

 large and stout, particularly the flexor of the terminal claw. The 

 first three pairs of feet possess a complicated musculature, as is well 

 shown in fig. 25, which makes them powerful propelling organs. 



Fig. 26.— Musculature of the 

 second maxillipeds op cali- 

 gus rapax. 



