MORPHOLOGY OF CYCLOPS. 41 



Poecilopoda) on the one hand, and Palcemon among the Decapoda on the other ! Using 

 this character a phylum may be constructed differing from the former only in the addition 

 of a new group " Bathypleura." 



This at once shows how the Branchiura (Argulus) come to he so close to Copepoda ; 

 they are a very slightly modified group that has come down from the time of the Eudi- 

 plopida, before further divergence had taken place from the Copepod stem. 



(d). The Retention of the Anal Respiration, and the Absence of Gills. — I regard this 

 as of capital importance. In almost all the Malacostraca the gills, or at least the 

 podobranch,can be traced to the Phyllopod or Leptostracan type. Here we find nothing 

 of the kind. In Cirripeds and Ostracods the gills are of totally different origin, and it 

 is just these two orders that we saw are referable to an archaic type intermediate 

 between the Copepoda and the Phyllopoda. If we substitute in our last phylum 

 " Podobranchiata " for " Protophyllopoda " it will express the facts thoroughly. 



The suggestion has occurred to me that the rectal part of the intestine was primi- 

 tively connected rather with the nephridial system than with the (then aproctous) gut, 

 an arrangement actually persisting in Platyelmia and some Rotifers {Asplanchna). In 

 confirmation of this view it is to be noticed that in some pelagic Mollusca, besides the 

 anal respiration as mentioned by Gegenbaur, a similar respiration takes place by the 

 adjacent renal organ, as (first indicated by Huxley, I believe) shown by Joliet, who has 

 conclusively disproved the taking-up of the water into the blood (' Comptes Bendus,' 

 1883). What seems likely is that this renal opening, adjacent to the primitively blind 

 end of the intestine, has fused more or less with it, and furnished it with an outlet, 

 which in Crustacea (and Annelida) has lost all connexion with the kidney, while in the 

 Mollusca a separation of this rhythmical organ into rectum and kidney proper has 

 taken place. The condition in Amphineura is strongly confirmatory of this view *. 



(e). Plasticity of the fore part of the Alimentary Canal. — As is well known, in the 

 Phyllopoda the gut has two branched or simple hepatic diverticula ; in Ostracods, Lep- 

 tostraca, and Malacostraca, besides this, the anterior part of the stomach is chitinized. 



Now we find in Cyclops and Diaptomus a chitinized anterior end of the stomach and 

 no diverticula ; in Calanus &c. the chitinization is limited to the gullet, and there is a 

 median dorsal branching hepatic diverticulum. In Temora and Calanella there are 

 paired caeca. The conclusion is that in various Copepoda we find a foreshadowing of 

 conditions well marked in the other Crustacea f. 



(f). The Condition of the Circulation. — The heart, when present in Copepoda %, is a 

 dorsal contractile sac, lying in the first or second thoracic segment, with three venous ostia, 

 one posterior and two lateral, and a median anterior arterial ostium, sometimes continued 

 into a short branching aorta ; this corresponds with the heart of Cladocera and the 

 cardiate Ostracods. Now, while I am perfectly aware of Claus's reasons for considering 



* Vide Lankester, " Mollusca," Encyclopedia Britanniea. 



t May not the chitinization of the gullet and stomach, with the development of an armature, be returns to a 

 primitive condition found in so many Worms and Rotifers, and even homologous, longo intervallo, with the odonto- 

 phore of Mollusca ? 



t Calanida; and Pontellida?. 

 SECOND SERIES. — ZOOLOGY, VOL. V. 6 



