Anatomy of certain Rotlfors. 43 



selected this species mainly on account of its size and also 

 because of the case with which one is able to study the 

 sections. I have, liowever, deemed it prudent to include in 

 my illustrations a nearly median transverse section through 

 themastax of Melicerta ringens. In this species (J/, ringens) 

 the cells in the hard parts of the tropin are perhaps better 

 shown than in M. conifera {vide PI. IV. fig. 4) . ^J'urning now to 

 the movements of the mastax, Mr. Gosse notices his previous 

 observations (6) and selects Limnias ceratophylli for a detailed 

 examination. He says : '* The mastax consists of three sub- 

 globose lobes . . . one on each side appro))riatcd to each 

 malleus, and a third descending towards the ventral aspect, 

 which envelopes the incus. The mallei are . . . intimately 

 united to the rami of the incus . . . each uncus forming, 

 with its ramus, a well-defined mass of muscle, enclosing the 

 solid parts, and in form approaching the quadrature of a 

 globe : two flat faces opposing and working on each other." 



My own opinion is that there is only one pair of muscles 

 prescjit in the mastax. On reference to PI. IV. fig. 3 it will be 

 seen that each half of the manubrium is connected with its 

 fellow by a comparatively thick arching band which stretches 

 over the dorsal region of the mastax. Attached to this band 

 on either side of the median line is a muscle, which 1 have 

 figured slightly more prominently than it really is in section, 

 which, running across each half of the ramus at an obtuse 

 angle, terminates at the extremity of the fulcrum {vide fig. 3, 

 frn). The movements of these various parts are as follows : — 

 By the simultaneous contraction of the preceding muscles the 

 rami are drawn upwards and inwards, and by the relaxation 

 of the same muscles the rami are forced apart by the semi- 

 circular band acting on them. 



1 may add finally that I have been unable to discover any 

 muscular fibres penetrating the mastax. 



ExcEETOEY System. 



Flame-cells or Vihratile Tags. 



Concerning the structure of these singular bodies there has 

 been and still exists a considerable difference of opinion. A 

 summary of our present knowledge concerning the structure 

 of these bodies with their lateral canals is given by Dr. 

 Hudson in his monograph, forming an appendix to the first 

 volume. His description is too long for me to give at length ; 

 it may, however, be briefly summarized as follows: — 



