G46 MR. J. E. DUEEDEK ON THE EEIiATIONS OE 



I have also been able to demonstrate the same for C onyrcia, and 

 Haddon and myself (1896, p. 152) for C. australis. Kwietniewski 

 (1896) makes no reference to those of O. carnea, Stud. 



Throughout its internal tissues, Bhodactis Sancti-Tliomcd bears 

 enormous horn-coloured nematocysts. So remarkable a feature 

 are they in sections that Prof. McMurrich (1889, p. 45) observes 

 that they looked almost like encysted nematode parasites. His 

 measuremeuts gave a length of about 68 jx and a breadth of 27 fx. 

 The vrall of the cyst is much thickened and bears spinous 

 projections, and the thread is finely striated. They occur in the 

 greatest numbers in groups in the lower part of the mesenterial 

 filaments and in the endoderm of the so-called disc-tentacles. 

 Those of Ricordea jiorida are a little smaller, but nevertheless 

 constitute a very distinct feature in sections through the lower 

 region of the polyp. It is a curious fact that McMurrich's 

 sections of Bahaman examples of this species contained no 

 nematocysts whatever, not even at the tips of the tentacles. I 

 find at least two kinds to be very abundant in Jamaican specimens — 

 a long narrow variety at the knobbed end of the tentacles, and 

 the large oval form in the internal tissues. Having directed 

 Prof. McMurrich's attention to the disparity, a more special 

 examination proved that the original statement was correct. Two 

 examples I have sectionized since agree with those from the 

 Bahamas in this entire absence of stinging-cells. 



Mesoglcea. 



The mesoglcea of the Actiniaria usually contains small stellate 

 or rounded cells distributed with approximate uniformity 

 throughout the fibrillar or clear homogeneous ground-substance. 

 Sometimes, as in the Zoanthese, it may, in addition, enclose cell- 

 islets, or become broken up by irregular canals, ingrowths from 

 the ectoderm or endoderm or from both. In most Sagartidse and 

 in some other Actiniae parts of the muscular system may also be 

 embedded within it. The middle layer of the Madreporaria, on 

 the other hand, is generally less developed and clear and homo- 

 geneous throughout, an isolated cell occurring but rarely. Thus 

 Bourne (1887, p. 18), who originated the term mesoglcea, 

 states : — " I could find no trace of structure in this layer 

 [mesoglcea] in Fungia, though it is possible that the use of 

 proper reagents in the fresh condition might have disclosed a 



