NO. 1788. NORTH AMERICAN ERGASILID^— WILSON. 283 



we should look for as a result of degeneration in the maxillae, but it 

 is radically different from anything that can be found in the way of 

 mandibular palps among either the parasitic or free-swimming forms. 



4. Finally the mandibles in the genera Tucca and Ergasilus and 

 in some species of Bomolochus already possess well-defined palps 

 attached where one would expect to find them, at the tips of the basal 

 joints and entirely distinct from these maxillae. Hence the latter, 

 if regarded as palps, would form a second pair on the same appendages 

 and attached at the very base of the basal joints — an untenable sup- 

 position. 



TTie second maxillse. — Burmeister and Heller are the only two 

 authors who have not agreed in calling this pair of appendages the 

 first maxillipeds. But the following considerations identify them 

 as maxillse and not maxillipeds. 



1. From the close relationship between the Ergasilida? and free- 

 swimming forms we should naturally expect the mouth-parts to 

 correspond in origin and development. By reference to figures 34 

 and 37 it will be seen that this penultimate pair of mouth-parts arises 

 in front of the suture which separates the head from the thorax, while 

 the last pair arises behind it. The latter appendages therefore are 

 thoracic in origin, and must be regarded as maxillipeds, while the 

 former are cephalic and are just as surely maxillse. 



2. The correspondence of this third pair of mouth-parts with the 

 second maxillse in free-swimmers is further shown by their relation 

 to the paragnaths in certain species (Bomolochus solese, Artacolax 

 sxtiger, etc.). The proximity of the base of the appendages to the 

 paragnaths shows them to be identical with the second maxillse 

 of free-swimmers. 



The maxillipeds. — Two facts have contributed to the confusion in 

 regard to these mouth-parts. In the females of the genus Ergasilus 

 they are entirely wanting, while in those of the genus Bomolochus they 

 are abortive in position, being attached outside, and partly in front, 

 of the other mouth-parts. 



These two discrepancies have bothered many observers and have led 

 to curious blunders. Burmeister failed to find them at all; Heller 

 states plainly that they correspond to the maxillary hooks in Caligus 

 and Lepeophtheirus; Bassett-Smith implies as much by designating 

 them as "hamuli" and then applying the same term to the true max- 

 illary hooks of Bomolochus (Irodes) tetrodonis. 



That they are really maxillipeds, as Claus, T. Scott, Brian, and 

 others have named them, seems conclusively proved by the following 

 considerations. 



1. Their position: The terminal hooks are situated far forward in 

 the Bomolochinse, even perhaps in front of the other mouth- parts, 

 but we can not regard the appendage as attached there. Its posi- 



