88 MARGARET 0. COLLCUTT. 



The Basal Ccenosarc of the Colony. — As meutioned 

 above_, this consists of two layers of ectoderm, enclosing be- 

 tween them a ramifying mass of endodermal tubes, and forms 

 that part of the colony which connects the polyps with one 

 another. The lower layer of ectoderm secretes the greater 

 part of the skeleton, forming a continuous layer in contact 

 with it; the upper layer of ectoderm also forms an unbroken 

 expansion, and is continuous with the ectoderm of the polyps. 

 The two ectodermal layers thus form two sheets of cells, one 

 above the other, and are in close contact with one another, 

 except where the tubes of endoderm are interposed between 

 them, such tubes serving to place the cavities of the polyps in 

 communication (PI. 1, fig. 1, c). 



These endodermal tubes are more or less oblong in cross- 

 section, and are always surrounded by a narrow layer of 

 mesogloea, which separates the endoderm from the ectoderm 

 (PI. 1, fig. 5), and is continuous with the mesoglaa of the 



polyps. ^xi-..]^.' 



At frequent intervals thread-like strands of mesogloea from 



the lower surface of this endoderm pierce the lower ectoderm, 



and attach themselves by slightly widened bases to the 



skeleton (PI. 1, figs. 1, c, and 5). 



Similar strands fix the polyps to the chitin, but these are 

 thicker, more numerous, and, since the lower ectodermal layer 

 is generally much shallower below the polyps, they are often 

 shorter. These processes thus exhibit the singularity of being 

 surrounded on all sides by ectoderm cells. Similar strands 

 are figured by Weismann (15) as attaching the ccenosarc of 

 Eudendiium ramosum to the perisarc. 



The lower ectoderm and the endodermal tubes penetrate 

 into and fill up the intercommunicating chambers and the 

 grooves of the large spines, the superficial ectoderm extending 

 over all. 



Strethill-Wright (10) and Allman (13) both mention the 

 fact that this basal ccenosarc is capable of communicatiug the 

 effect of any shock it may receive to the various members of 

 the colony. 



