290 K, E. ZIMMEKMANX. 



the epistomial ridge, appears to constitute a very efficient filter by 

 which particles are rejected at the entrance to the branchial chamber 

 itself. [X.B. — In specimens examined, the hairs of this strainer are 

 muddy.] 



The in-current, on reaching the posterior part of the prostomial 

 chamber, must be slightly aflected by the presence of the dorsal 

 V-ridge, which, however, seems to be not of sufficient importance to 

 change the course of the whole body of the current. The main mass 

 of the current doubtless sweeps on, is split into right and left streams 

 along the arms of the inverted V formed by the apophyses of the 

 mandibles, and enters the branchial chambers ; meanwhile the small 

 secondary current produced by the influence of the epistomial ridge 

 flows out ventrally through the gap in the hairy ventral wall of the 

 prostomial chamber, sweeping away in its course such particles of 

 mud, etc., as have been prevented by the hairy sieve from entering the 

 branchial chambers with the main current. 



SUMMAEY. 



Corystes buries itself in sand for protection, with the tip of the 

 antennal tube, through which enters the respiratory current, projecting. 

 The water which enters the antennal tube cannot be quite clear : there 

 is a hairy filter, which rejects particles of mud, etc., at the entrance 

 to each branchial chamber. The main body of the in-current is split 

 into right and left currents, owing to the position of the apophyses of 

 the mandibles, and these two currents enter respectively the right and 

 left branchial chambers. The epistomial ridge on the roof of the 

 prostomial chamber turns aside some portion of the in-current, which 

 portion passes out ventrally through a gap in the floor of the chamber, 

 carrying out with it foreign particles brought in by the in-current 

 and rejected by the sieves guarding the entrances to the branchial 



chambers. 



EXPLANATION OF PLATE V. 

 Fig. 1, Front end of body of Corystes cass^ivelaunus, ventral view. 



a. incompleteness in bairy floor of prostomial chamber. 

 Fig. 2. View of prostomial chamber from ventral side after removal of most of the 

 mouth appendages. 



a. epistomial ridge, fringed with hairs. 



b. labruni. 



c. entrance to branchial chamber of left side. 



d. mandible. 



Fig. 3. Diagram longitudinal section a little to one side of the median line. 



a. position of antennal tube. e. hairs flooring prostomial chamber. 

 6. prostomial chamber. /. position of maxillae. 



c. hairy strainer. g. gap in the hairy floor. 



d. branchial chamber. 



