REVIEW OF GENUS ARGULUS MEEHEAN 461 



Martin has shown that the development of the buccal cavity is 

 from the basal segments of the mandibles and the lower and upper 

 lips. Reason indicates that the maxillae would have to develop be- 

 tween the upper and the lower lip in order to be in the proboscis. 

 This would be contrary to maxillary development in other Crustacea 

 where the maxillae lie behind the under lip. On the Caligoidea the 

 first maxillae are near the base and lateral to the second antennae, 

 and the second maxillae are at the sides of the suctorial tube. 



Scott and Scott (1913) state that in copepods the various append- 

 ages develop in regular order and in the parasitic forms may then de- 

 generate. These appendages include two pairs of maxillae and a pair 

 of maxillipeds. No one has shown in a satisfactory manner that all 

 these ever occur on argulids. On the basis of the above evidence it 

 was decided that the two pairs of appendages between the mandibles 

 and the first swimming legs should be called maxillae, with only the 

 mandibles in the buccal cavity. 



Among the argulids the body is depressed, as a result of adaptation 

 to their parasitic existence on the external surface or in the gill cavi- 

 ties of fishes. The carapace (fig. 21, 5) is composed of lateral lobes 

 or alae, which originate as folds of the posterior region of the cepha- 

 lon and are fused to the dorsal surface of the first segment of the 

 thorax. Dorsally the cephalon proper is separated from the first 

 thoracic segment by a transverse groove. Extending obliquely from 

 this groove on each side is a ridge, which sets off the cephalic area 

 and more distally extends outward on the carapace as a groove 

 ending at the edge in a slight sinus. 



Extending forward from the transverse groove on the middorsal 

 surface of the carapace is a pair of ridges lying close together, the 

 dorsal ridges, which pass between the eyes and end some distance 

 forward. They may either be parallel or bow toward each other 

 just posterior to the eyes and away from each other just ahead of 

 the eyes. A median "nauplius eye" may be seen between the ridges 

 just anterior to a transverse groove or ridge some distance posterior 

 to the compound eyes. On two American fresh-water species the 

 dorsal ridges are branched at the anterior end; others are simple. 



The alae extend backward over the thorax, leaving a sinus that 

 exposes the three free thoracic segments between them. These lobes 

 may extend to the third swimming legs or far enough back partially 

 to cover the abdomen. They may partly close the sinus by overlapping 

 slightly, as on some species where the alae extend over the abdomen, 

 or they may flare out leaving the sides of the sinus diverging. 



The abdomen is unsegmented and bilobed at the posterior end, 

 forming the anal sinus. The anus is found at the base of this sinus, 

 while somewhere along the inner edges is a pair of anal furcae. 



