BRANCHIOPODA. 121 



March — they acquire another pair of feet, constituting; the genus 

 Naiiplius, Muller. After the first change they have the form and all 

 the parts which characterize the adult animal, but more exiguously 

 proportioned; their antennae and feet are proportionally shorter. 

 After thrice changing their skin they are capable of propagation. 

 Most of these Entoniostraca swim on their back, dart about with 

 great vivacity, and move both backwards and forwards with equal 

 facility. For want of animal substances they will attack vegetable 

 matters, but the fluid in which they live does not pass into their 

 stomach. The alimentary canal extends from one extremity of the 

 body to the other. The heart in the C. castor is oval, and situated 

 under the second and third segment of the body; a vessel is given off 

 at each of its extremities, one running to the head, and the other to 

 the tail. Directly under it is a second analogous, but pyriform or- 

 gan, which also produces a vessel at each end, corresponding per- 

 haps to the branchio-cardiac canals, mentioned in our observations 

 on the circulation of the Crustacea Decapoda. From several expe- 

 riments made by Jurine upon various Cyclopes, alternately asphyxi- 

 ated and resuscitated, it would appear that in this sort of resurrec- 

 tion the extremity of the intestinal canal gives the first signs of life, 

 and that the irritability of the heart is less energetic; that of the an- 

 tennae, in the males especially, of the palpi, and lastly of the feet, is 

 inferior. No alteration is efflected in the antennae by amputating a 

 portion of them; the reintegration takes place under the skin, for the 

 organs reappear in all their entireness at the ensuing moult. 



The C. staphylinus, from its shorter antenn^, the superior of which 

 consist of a considerably less number of joints than those of other 

 Cyclopes, while the inferior, on the contrary, have more; and from 

 the shape of its body which gradually diminishes towards its poste- 

 rior extremity, so that it seems to have no tail or at least none that 

 is abruptly formed, and its back, in the females, being armed with 

 a kind of horn posteriorly arcuated, forms a particular division. The 

 C. castor, and some others whose inferior antennae and mandibular 

 palpi are divided above their base into two branches, may also com- 

 pose another group. The one designated by Leach under the gene- 

 ric name of Calanus, might in fact constitute a separate subgenus, 

 if it were true that the animal on which it is founded had no inferior 

 antennae; but has that gentleman satisfied himself that such is the fact, 

 by personal observation, or does he depend upon the assertion of 

 Muller? 



C. quadricornis; Monoculus quadricornis, L. ; Mull., Entom., 

 XVIII, 1 — 14; Jurine, Monoc, I, II, III. All the antennae sim- 

 ple or undivided; the inferior with four joints, and their length 

 Vol. III.— Q 



