142 



Section 3. Poecilostoma. 



General Characters. Anterior antennae in male not hinged. Posterior 

 antennae without any outer ramus, and generally adapted for prehension. 

 Oral parts not adapted either for mastication or for suction. Mandibles 

 wanting. Maxillae with the terminal part variously modified for conveying 

 food to the mouth, and provided outside with a flap-shaped setiferous palp or 

 exopodite. Anterior maxillipeds never prehensile. Posterior maxillipeds trans- 

 formed in male to powerful grasping organs. Natatory legs, as a rule, well 

 developed. Last pair of legs, when present, extended laterally, uni-or biarticulate. 



Remarks. The Cyclopoids comprised within this section differ materi- 

 ally from those included in the 2 preceding sections by the structure of the 

 mouth-organs, which are not adapted either for mastication or for suction, 

 but more properly for licking up finely dissipated nourishing particles from 

 the surface of various organisms or from the wall of their inner (branchial) 

 cavities. In accordance therewith the chief masticating organs, the mandibles, 

 are entirely wanting, and the number of oral appendages of course reduced 

 to 3 pairs only, viz., the maxillae and the 2 pairs .of maxillipeds. I am 

 well aware that the above interpretation of the mouth-organs, which agrees, 

 as will be seen, with that originally set forth by Thorell, is quite at vari- 

 ance with the view generally adopted by recent carcinologists on the autho- 

 rity of Glaus, according to which the usual number of oral limbs should be 

 present, the foremost of them representing the true mandibles. There are, 

 however, several serious objections to be urged against the correctness of this 

 altered view of the oral apparatus. Indeed, on a careful examination of the 

 mouth-organs in various types of the present section, I am led to the con- 

 clusion that the view insisted on by Glaus and accepted by most recent authors 

 cannot be maintained, and that we must recur to the interpretation originally 

 given by Thorell as the only one acceptable. 



As to the number of oral Iftnbs, only 3 pairs are in reality disting- 

 uishable, as stated by Thorell. The assumption of the presence of a 4th pair 

 between the 2 anterior ones rests entirely on a miscomprehension, a part 

 of the foremost pair having been erroneously taken for an independent limb. 

 This part, generally described as a maxilla, is always found firmly attached to 

 the outer side of the foremost pair of limbs, and represents in reality, as opined 

 by Thorell, the palp or exopodite of those limbs. Though in a few cases 

 this exopodite may assume a somewhat maxilla-like appearance, it presents 



