282 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



This furnishes a strong argument in favor of the community of ori- 

 gin of the appendages themselves. 



This question can be definitely settled only in the same manner 

 as was the origin of the two posterior pairs of appendages. Some 

 species possessing these lateral hooks will give us a larva on whose 

 body the two appendages in question can be traced to their origii>. 

 In the meantime we can only say that the hooks in the Ergasilidse 

 certainly correspond to the similar appendages in the Caligidae. 



They appear to be situated farther forward, but this is largely due 

 to the backward migration of the mouth-parts. For the present, 

 then, we are justified in calling them maxillary hooks and in regard- 

 ing them as closely related to the first maxillae. 



The first maxillae. ^-These were first described for the genera 

 Bomolochus and Eucanthus {Anchistrotos) by Claus in 1864 who 

 designated them correctly as maxillae, and they have been thus 

 recognized in these genera by all subsequent investigators. In 1875 

 Claus described the corresponding appendages in the genus Ergasilus 

 and called them also maxillae. 



But in this latter genus they have been either overlooked by other 

 authors, or when seen (Gadd, 1904) have been regarded as palps of 

 the mandibles. That they are distinct appendages, although very 

 rudimentary, appears certain from the following considerations: 



1. In the genera Tucca and Taeniacanthus this pair of mouth- 

 parts is separated by a considerable interval from those on either 

 side of them. The space is wide enough to show that they are not 

 attached to any other pair. But the fact that they are distinctly 

 separate appendages here furnishes a strong argument that they 

 are also separate in the other genera. Their juxtaposition is the 

 result of a crowding together of the appendages during their back- 

 ward migration, and does not indicate actual union. 



2. Again, there is altogether too close an agreement in size, shape, 

 position, and armature between these organs in the different genera, 

 and in the two sexes of the same genus, to allow us to consider them 

 as palps. Palps vary greatly in different species, to say nothing of 

 different genera, and they usually show marked sexual variations. 

 These appendages are not only present, but are practically identical 

 in every species throughout the entire family, and thus furnish good 

 proof of their disconnection. 



3. Among the Caligidae this pair of maxillae show marked degen- 

 eration; the exopod is reduced in size and much simplified, while the 

 endopod has degenerated in some species to a mere knob, armed with 

 one or two setae. Here in the Ergasilidas the exopod has entirely 

 disappeared from all the species if it is not to be found in the maxil- 

 lary hooks, as just suggested, and the endopod has degenerated into 

 a knob armed with setae. The structure therefore is exactly what 



