METAZOA COELENTERA. 119 



plainly seen with the microscope ; they extend crosswise, 

 as do also the long axes of the spicules. Occasionally, 

 according to Hickson, they project into the cavity of the 

 coral animal and look like the so called " septa " of 

 Syringopora. No true septa are developed in Tubipora 

 but within the tubes are found variously shaped tabulae, 

 some flat and others funnel-shaped. It is an interesting 

 fact that at the free end of the zoon the spicules are sep- 

 arate as they were in the single form that started the 

 colony. 



The danger of multiplying species that really do not 

 exist in nature has recently been pointed out by Hickson, 1 

 who states that the principal character which has been 

 used for distinguishing species of Tubipora is the diameter 

 of the zoQn walls, "and this character in every specimen 

 depends entirely upon the situation on the reef in which 

 it happened to grow." "Our desire to make new species," 

 says this author elsewhere, "seems to have blinded us to 

 what is perhaps the most important feature of Zoophytes 

 the infinite variety of growth they may exhibit to meet 

 the varying conditions of their existence." 2 



Parakyonium elegans M.-Ed. & H., (No. 168) is a colo- 

 nial form with a spicular skeleton. The lower, stem-like 

 portion is more dense than the upper part. and is without 

 zoons, while the small branches which are given off from 

 the upper portion are covered with zoons. Most of this 

 part can be withdrawn to the stem. The zoons have very 

 long tubes which can be seen in a vertical section extend- 

 ing from the stem to the surface. Surrounding these is a 

 thick coenenchyma which reaches up to the retractile por- 

 tion. The body cavities communicate with one another 

 by a system of nutritive canals. Alcyonium palmatum 

 Pallas (No. 169, the remaining Alcyonaria are placed, on 



1 A. Willey, Zoological Results, part 4, Apr., 1900, p. 493. 

 8 Trans, and Ann. Rep. Manchester Micr. Soc., Address of Presi- 

 dent, 1899. 



