40 PROF. M. M. HAETOG ON THE 



of Nebalia approach a rudimentary Copepod condition, the two hindermost possessing a 

 true sternal coupler. And in the Phyllopods themselves the limhs pass through a bifid 

 condition, equivalent to the same embryonic stage of the Copepod foot or rnaxillse in 

 its second state. 



A glance at the figures of niaxillge of various Copepods will show what I mean. The 

 only conjecture possible is that a metamorphosis similar to that which the maxillae are 

 undergoing in this group has extended backward to a variable number of segments in 

 the Protophyllopoda to adapt them to their limicolous life, and to make a stronger nutri- 

 tive current for their bodies, as they become more and more enclosed by the prolongation 

 upwards of the pleural groove in the thoracic region, and possibly its ultimate conversion 

 into a bivalve shell. 



5. Maxillipeds. — The complete separation of the two rami is comparable to that of the 

 same and the preceding pair of appendages in the Phyllopoda proper, where, however, 

 they are very much reduced. 



6-9. Thoracic Limbs. — These are, I believe, very primitive, and derived, like all the others, 

 save perhaps the antennules, from the limb of the Chsetopod *, pushed down by the exten- 

 sion of the tergal region, so that the notapodium becomes the exopodite, and the neura- 

 podium the endopodite. The couplers are purely Copepodan, reappearing, however, in the 

 hindermost abdominal legs of Nebalia (Claus). This is surely a strong confirmation 

 of the above stated view of the gradual extension of the " phyllopodization " of the limbs 

 from before backwards. 



10-11. Rudimentary Feet. — These are two pairs, sometimes used as accessory genital 

 organs, which remain in a very embryonic condition ; they serve as an index to the 

 process by which the abdomen has lost its appendages to make it a more efficient rudder. 

 As mentioned above, the coincidence in the position of the genital aperture here with 

 that of the female Leptostraca and Malacostraca brings the latter groups directly under the 

 succession of the Copepoda, putting the Phyllopods on one side, out of the direct pedigree 

 of the Malacostraca. 



12. Furca. — This, as I have already suggested elsewhere, is possibly a modification of a 

 pair of limbs. It is not present in the youngest Nauplius, but appears as a pair of 

 ventral outgrowths after the first moult. These are, perhaps, not developed in all Crus- 

 tacea, but exist, much reduced, as part of the Astacine " telson." It is interesting to note 

 their immense size in Nebalia. 



(c). The Copepoda may have their bodies flattened, with the pleurae straight out; but, so 

 far as I know, no member of the group has the pleural groove prolonged so far up the body 

 as to mark out an epimeral region between the reflection of the pleura and the sternum. 

 The development of the pleural cavity, when carried to an extreme, results in the forma- 

 tion of the bivalve shell ; and we have seen how in Ostracoda, and jwesumably in the 

 bivalve Phyllopods &c, the adductors really represent the suspensors of the entosternite, 

 which we know to be so primitive a structure as to be found in Arachnida (including 



* In the free-swimming pelagic Chsotopod Tomopteris the parapodia are 'well marked off from the body so as to 

 have a distinct protopodite ; and the hinder part of the body is tapering, with much reduced appendages, recalling or, 

 better, foreshadowing the Crustacean body. 



