1 06 HTDROZOA, 



the interesting discovery that many of the cham- 

 bers have an additional opening, by which they 

 communicate directly with the exterior. These 

 apertures are situated in the proximal or upper 

 wall of the chambers, along a line about midway 

 between that of the openings just described and 

 that of the vertical plate of the pneumatocyst. Of 

 the thirteen apertures observed by Kolliker, six 

 lay on one side of the vertical plate and seven on 

 the other; one aperture lies in the wall of the 

 central chamber, the other six at tolerably even 

 intervals between this and the margin. Conse- 

 quently, as there are more than six concentric 

 chambers, some of them must communicate with 

 these stigmata only indirectly." To the under 

 surface of the five or six innermost chambers are 

 attached from ten to fifteen elongated hollow pro- 

 cesses containing air, the pneumatic filaments 

 already mentioned. 



But complicated as the pneumatocyst of Velella 

 may seem, not less so is its curiously modified so- 

 matic cavity. On all sides the limb is traversed 

 by an anastomosing system of canals, which are 

 ciliated, and communicate with the cavities of the 

 phyogemmaria and large central polypite. Within 

 the roof of the latter, close beneath the pneuma- 

 tocyst, is lodged a peculiar brownish mass, the so- 

 called liver. This, also, is furnished with a canal 

 system of its own, which eventually becomes con- 

 tinuous with the sinuses of the limb. 



In addition to the preceding organs Velella pos- 

 sesses certain large " glandular sacs," for the dis- 

 covery of which we are indebted to Vogt. He 

 describes them as presenting a very curious minute 

 structure, and as arranged in a single series around 



