SEA-FISHERIES LABORATORY. 419 



of the maxillipedes. The extremely active motion of 

 these iiagella is quite obvious, and they probably 

 form an accessory current-producing organ of no mean 

 importance. 



The normal current, as we have seen, flows from 

 behind forwards, entering at the inhalent apertures and 

 leaving by means of the exhalent aperture. In Corystes, 

 Atelecyclas and Portumnus, Garstang* observed that the 

 branchial current was sometimes reversed. Bohnt has 

 extended these observations, and finds this phenomenon is 

 of universal occurrence throughout the Brachyura. In 

 Cancer the habit of reversing the branchial current does 

 not appear to be very strongly developed. Bohn suggests 

 that the reversal takes place in order to rest the fatigued 

 muscles of the scaphognathite, as the energetic action is 

 performed by different muscles in the two cases. 



The nabella (epipodites) of the maxillipedes pass 

 backward into the branchial chamber. That of the first 

 maxillipede (f.m. 1 ) is by far the largest, and extends 

 backward throughout the whole length of the branchial 

 chamber lying upon the gills. The flabellum of the 

 second maxillipede (/.m. 2 ) lies below the gills towards the 

 dorsal side of the epimera. It only extends as far forward 

 as the middle of the epimeron of the fourth thoracic 

 somite. The flabellum of the third maxillipede (f.m. 3 ) 

 also lies below the gills and on the ventral and outer side 

 of the second flabellum. Its proximal portion forms part 

 of the anterior boundary of the anterior inhalent aperture. 

 It extends backward to the posterior end of the epimeron 



* Garstang. " The Habits and Respiratory Mechanism of Corystes 

 cassivelaunus."— Journal Marine Biological Association, Vol. IV 

 (N.S.), p. 223. 



"The Respiratory Phenomena of Portumnus 7iasutus." Journal 

 Marine Biological Association, Vol. IV (N.S.), p. 402. 



t Bohn, G. "Sur la Respiration des Decapodes." Bull. Sci. 

 France et Belg. T. XXXVI (Ser. 6), 1902, p. 178. 



DD 



