FreUminary AccoiDit of Syniiie Pidchella. 3 



shows a nmnber of circular spaces scattered at intervals, 

 generally, but not always, in a single row. These are the 

 gastral cavities of the Sycon individuals cut across. Each is 

 completely surrounded by the thinible-shaped flagellated 

 chambers, or radial tubes, which radiate outwards from the 

 gastral cavity. On the adjacent sides of two neighbouring 

 gastral cavities the radial tubes are shorter than on the 

 outer sides. 



The inhalant pores are not visible to the naked eye and 

 are merely narrow interstices between the outer spicules 

 of the cortex, leading into irregular canals which pierce the 

 cortex to reach the flagellated chambers, exactly as in life 

 argentea. At their lower ends the gastral cavities of the 

 fused Sycon individuals communicate with one anothei-, 

 indicating that this peculiar form of Sycon colony has arisen 

 from fusion of adjoining individuals of a branching colony 

 such as Sycaw.lra arhorea. 



The flagellated chambers or radial tubes are approximately 

 octagonal in transverse section, while the much smaller inter- 

 spaces between them are square. The gastral (exhalant) 

 openings of the chambers are protected by very well 

 developed membranous diaphragms. Each gastral cavity 

 has also a single large well-developed diaphragm situate just 

 within the osculum. 



The Skeleton. 



The skeleton, as in Ute argentea, is very complex and 

 may be divided into Cortical, Tubar, Gastral and Oscular 

 portions. 



The Cortical Skeleton. — This consists (1) of very large, 

 fusiform oxeote spicules, slightly curved, fairly symmetrical 

 in shape and gradually and .sharply pointed at each enti. 

 Size when fully developed up to about oO by 014 mm. 

 These are arranged })arallel to the long axes of the gastral 

 cavities and in several layers ; (2) Between the above are a 

 few smaller oxea and great numbers of comparatively small 

 triradiates. The latter although api)arently disposed in the 

 utmost confusion and frequently of irregular shape, generally 

 show a marked tendency towards the sagittal type, the oral 

 angle being decidedly wider than the lateral. The rays are 



