ON THE STRUCTURE OF IIYDRACTINIA ECHINATA. 81 



described as '^ eggs " he now designates '^ sporosacs/^ and 

 asserts that the skeleton is external and similar to that of 

 Campanularia and Tubularia. Tlie reproductive polyps 

 have no mouth and only rudimentary tentacles. He confuses 

 Hydractinia with Podocoryne^ and distinguishes three 

 new species of Hydractinia. 



Hincks (12), in 1868, also mentions tentacular polyps; he, 

 as well as Strethill-Wright, describes fixed reproductive sacs. 

 He speaks of the basal coeuosarc as consisting of " a number 

 of anastomosing tubular stolons closely packed together, and 

 tilling in the tubular orifices of the chitinous skeleton, which 

 latter appears to consist of a series of tubes laid side by side 

 on a plate of chitin, and closely appressed one to the other." 



AUraan (13), in 1871, published a full account of Hy- 

 dractinia, in which he affirms that the basal part of the 

 colony consists of a number of closely approximated chitinous 

 tubes containing coenosarc, which consists mainly of endoderm 

 with only a thin investment of ectoderm, the latter secreting 

 the chitin. " At the free surface of the coenosarcal expansion 

 its intercommunicating canals are only partially invested by 

 chitin, this excretion being in the superficial layer of canals 

 confined to the deeper parts, thus forming open channels in 

 which the canals are lodged, so that when the soft parts are 

 removed the chitinous perisarc forms on the surface a multi- 

 tude of intersecting ridges, having between them the channels 

 which had contained the superficial coenosarcal canals. Upon 

 the whole of the free surface, however, the ectoderm of these 

 canals forms a continuous and very conspicuous layer, having 

 acquired increased thickness and developed in its substance 

 abundance of thread-cells. The whole free surface of the 

 common basal expansion of the colony thus presents an abso- 

 lutely naked layer of ectoderm. . . . There can be no doubt 

 that the whole hydrophyton of Hydractinia must be re- 

 garded as consisting of a set of coenosarcal, freely intercom- 

 municating tubes, which have excreted from their free surface 

 a chitinous perisarc, and have intimately coalesced with one 

 another." 



VOL. 40, PART 1. — NEW SEE. F 



