THE PYKOSOMA. 



325 



Kew bodies among the forms of animal life exhibit such exquisite 

 figures as those which we see displayed in the combinations of 

 these compound Ascidians." 



In the genus Diazona, which has its chief seat in the Mediter- 

 ranean, the animals, which are very prominent and arranged in 

 concentric circles, form a single system expanded into a disc like 

 that of a flower or of an Actinia. The anal orifices, it will be 

 seen, are situated close to the branchial apertures at the free end 

 of the single animals, while in the Botrylli 

 they open into a central excretory cavity. 



In the Pyrosomes we find large co- 

 lonies of small individuals aggregated in 

 the form of a cylinder open at one end. 

 Their mouths or anterior extremities are 

 situated on the exterior of this hollow 

 body, which they bristle with large and 

 longish tubercles (a), whilst the opposite 

 or anal orifices (b) open into the cavity 

 of the cylinder, whose smooth wall they 

 perforate with numerous small holes. By 

 a simultaneous action the central cavity is 

 either narrowed or enlarged, and by this 

 means the strange social republic glides 

 slowly through the waters. 



The Pyrosomes inhabit the Mediterra- 

 nean and the warmer parts of the ocean. 

 In the former at times their abundance is 

 a source of great annoyance to' the fisher- 

 men, sometimes even completely clogging 

 their nets, and on the high seas they are 

 not seldom met with in almost incredible 

 profusion. Their delicate and transpa- 

 rent forms, their elegant tints, and their 

 unrivalled phosphorescence render them 

 objects of admiration to the voyager, and 

 entitle them to rank amongst the most 

 resplendent living gems of the ocean. 



While the sessile Ascidise remind one 

 transparent Salpse, freely swimming in the sea, bear a great 

 resemblance to the pellucid jelly-fishes. Each resembles a 



A single individual of 



Pyrosoma giganteum, cut 



out of the common test 



and magnified. 



u. Branchial or external ori- 

 fice. 

 b. Anal or internal orifice. 

 d. Stomach. e. Liver. 



/. Branchial. 



of the polyps, the 



