TUBULARIA SOLITARIA. 89 



I rejj'avd tlie canals as being for the purpose of conveying 

 down to the tuber nutritive fluids, which are ehiborated by 

 the endoderni cells into the globules so abundantly stored 

 up in the tuber. 



The ectoderm below the perisarc groove is of considerable 

 thickness. In sevei'al specimens which were sectioned, but 

 not in all, the ectoderm, especially in this region, Avas crowded 

 with large granular bodies (fig. 14, (j.rii.), which stain with 

 much intensity with ha3matoxylin. The bodies were of irre- 

 gular shape^ and some of them, especially those in the neigh- 

 bourhood of the mesoglea, were apparently in the condition 

 of breaking up into small granules. These bodies stain 

 similarly, and have quite the same aspect as the bodies 

 marked g. in. in fig. lo, or pr. in fig. 5. I consider it 

 probable that active growth was taking place in this region, 

 and that the bodies in question are coagulated albumens or 

 some other substances, which had been passed out through 

 the mesoglea into the ectoderm. 



In the ectoderm of the hydrorhiza and the tubers the 

 wedge-shaped cells are characterised by being finely granular 

 iu nature, and in this respect they resemble the cells forming 

 the perisarc groove (fig. 16). It is probable that these cells 

 still retain their power of secreting- perisarc substances. 



It would be interesting to ascertain whether there is any 

 symbiotic or parasitic interaction between the hydroid and 

 the sponge further than the mechanical support rendered by 

 the latter to the former. The sponge appears to attempt to 

 shut itself off as much as possible from the hydroid ; the 

 tissues of the sponge in the immediate neighbourhood of 

 the hydroid are denser and more fibrous than further in, thus 

 forming a kind of cyst-wall (fig. 16 s. p.). 



(3) Gonosome. — The gonophores spring in clumps of 

 three to five from short semi-erect peduncles (or blastostyles) 

 (fig. 5 ped.), which arise from the hydranth just above the 

 verticil of basal tentacles. A gonophore originates as a 

 swelling or out-pushing from the peduncle. The ectoderm 

 at the apex of the swelling thickens, and the endoderm grows 



