518 BIOLOGY. 



oviform, with respiratory lamellae upon the absorbent 

 tubes, Rippenquallen or Beroes. 



3183. An Acalephan is a brood-egg, which swims 

 freely about without a shell. 



3184. The vessels are quaternary in their distribution, 

 and form a cross, like the involucral vessels of the chick. 



3185. In these animals the ova first begin to be de- 

 tached and agglomerated together in definite situations 

 so as to constitute ovaria. The number here is also four. 



They lie usually within four cavities surrounding the 

 stomach, and into these wide apertures situated near to 

 the mouth lead ; they are at the same time regarded as 

 respiratory cavities. 



In other species vesicles, wherein seminal animalcules 

 are developed, occupy the same situation. Here there- 

 fore is recognised for the first time a separated sex. 



In the Rohrenquallen or Physalise the ovisacs mostly 

 depend externally in the form of bells. 



Besides this we find in the Acalephea all sorts of laminae, 

 which are probably organs of respiration. 



It is not known what is the meaning of the air-sacs 

 and of what the air consists. 



Most of the species emit light like globes of fire, just 

 as many Infusoria do also. It is probably a phospho- 

 rescence given out by the mucus when passing over into 

 a state of decomposition. 



Very many have also the stinging property of the 

 nettle ; but, whether the cause of this is chemical or me- 

 chanical, is not yet exactly known. 



SECOND CIRCLE. VASCULAR, SEXUAL ANIMALS. 



3186. So far, or in the ascending scale up to the Aca- 

 lephae, the animal is only viscus with an absorbent 

 canal, which is at the same time a canal of evacuation, 

 without a distinct intestine being set apart for that pur- 

 pose ; such is the general rule. 



3187. After the Acalephae the formation undergoes a 

 change ; the distinction between the exterior and interior 

 is prominently displayed, and the internal wall becomes 



