REPORT ON THE SIPHONOPHOR^E. 35 



identical with that of a simple Medusa ; the central union of the former is connected by a 

 pedicular canal with the gastral cavity of the gonostyle. (8) The system of the 

 tentacular canals or the simple peripheral vessels which arise from the periphery of the 

 subumbrellar system and pass into the tentacles. 



Besides these eight parts of the canal system there occurs often (9) a coronal canal, 

 or a horizontal circular ring-canal placed in the coronal groove of the umbrella, between 

 the margin of the pneumatocyst and the centradenia. It represents an inner annular 

 vessel which carries on the circulation in the canals of the centradenia and the sub- 

 umbrella. The entoderm al epithelium exhibits a very different and remarkable shape in 

 these different systems of gastro-canals. The most important seems to be the rich 

 production of black or dark brown bdious granules in the hepatic vessels, and of green 

 guanin crystals in the renal vessels. 



Eegarding the morphological value of these different parts of the gastro-canal system 

 of the Disconectae, and comparing them with the corresponding parts of a simple octo- 

 radial Medusa (Trachynemida), we may arrive at the following important conclusions : — 



(1) The eight primary perradial canals, which arise from the base of the stomach (of the 

 central siphon) and run in the subumbrella towards the margin, are homologous with the 

 eight subumbrellar centrifugal radial canals of a simple Trachynemid (e.g., Pectanthis). 



(2) The marginal ring-canal, which connects the former and runs along the limb of the 

 umbrella inside the series of marginal glands, is homologous with the usual marginal 

 canal of a simple Medusa. (3) The tentacular canals, which arise from the subumbrellar 

 canals and pass into the tentacles, are comparable to the tentacular canals of those 

 Medusae which possess submarginal tentacles (e.g., Drymonema). (4) The gonostylar 

 canals, which arise from the subumbrellar canals and pass into the cavity of the gonostyles, 

 are homologous with the cavities of the eight genital sacs of a Trachynemid. (5) The 

 eight centripetal radial canals, which arise from the coronal canal, run in the upper face 

 of the centradenia to its centre and there unite into a " liver star," may be compared to 

 the centripetal canals of the subumbrella of Carmarina, Pectyllis, and other Trachy- 

 medusae. (6) The coronal canal, or the inner ring-canal, which runs in the coronal 

 groove on the margin of the pneumatocyst, may be compared to the inner ring-canal 

 which develops by anastomoses of the radial canals in some Medusaa. 



Whilst these parts of the canal system of the Disconectae may be compared to corre- 

 sponding parts of simple Trachyrnedusse, there are other parts which are quite peculiar to 

 the former. These secondary productions are : — (1) The pallial system or the anasto- 

 mosing radial canals of the exumbrella, which form a network on the upper face of the 

 pneumatophore. (2) The internal reticular canal system of the centradenia, forming a 

 hepatic plexus in its upper and a renal plexus in its lower half. The development of the 

 superficial pallial system of canals is a consequence of the invagination of the apical part 

 of the exoderm which produces the pneumatosaccus. The development of the internal 



