latinous, diaphanous, and move nearly in the manner of a Medusa, 

 The receiver produces from the bottom of its cavity a chaplet which 

 traverses a semi-canal in the received, and appears to be composed of 

 ovaries, tentacula, and suckers, like those of the preceding genera. 



This genus has been divided by Messrs, Quoy and Gaymard ac- 

 cording to the relative form and proportions of the two individuals. 



Thus in 



DiPHYES, proper. 

 The two individuals are almost similar and pyramidal, with some 

 points round their aperture, Avhich is at the base of the pyramid *. 



In Calpes the received is still pyramidal, but the receiver is very 

 small and square. 



In Abyles the received is oblong or oval, and the receiver some- 

 what small and bell-shaped. 



In Cuboides the received is small and bell-shaped, the receiver 

 much larger and square. 



In Navicula the received is bell-shaped; the receiver is large, but 

 has the figure of a wooden shoe f. 



There are several other combinations. 



CLASS IV. 



POLYPI {a). 



Our fourth class of the Radiata or Zoophytes has been thus named 

 because the tentacula which surround their mouth give them a slight 

 resemblance to an Octopus called Polypus by the ancients. The 

 number and form of these tentacula vary. The body is always cy- 

 lindrical or conical, frequently without any other viscus than its ca- 

 vity; and frequently also with a visible stomach, to which adhere intes- 

 tines, or rather vessels excavated in the substance of the body, like 

 those of the Medusae; in this latter case we usually find ovaries also. 

 Most of these animals arc capable of forming compound beings, by 

 shooting out new individuals, like buds. They also, however, propa- 

 gate by ova, 



* Bory Saint Vincent, Voy, aux Isles d'Afrique. 

 ■f See the Mem. of MM. Quoy and Gaym., Ann. des Sc. Nat,, X, 



{j:;^ («) This class of animals, although nearly at the end of the series, is one of the 

 largest, and certainly the most singular of the whole. Such is the enormous accu- 

 mulation of the stony envelopes formed by them in certain seas, that islands are pro- 

 duced, coasts extended, and harbours blocked up by them. Tl,e late lamented M. de 

 Lamarck has even hazarded the idea, that the calcareous strata of the globe may 

 have been produced by them. Polypi were formerly considered as stony plants. 

 Tmperati (1699) was the first who doubted their vegetable nature, and Trembley's 

 observations on the Hydra (1740) put the question at. rest. Since that period, our 

 knowledge of them has been considerably increased by the labours of Ellis, Boccone, 

 Cavolini, Laraouroux, Sue. &c. — Eng. Ed. 



