16 PERCY SLADEN TRUST EXPEDITIONl 



Haddon and Shackleton (57) observed nematocysts in the endoderm of Isaurus 

 asymmetricus and of Zoanthus copjDingeri ; those figured on PI. 64, fig. 2 bear 

 a certain resemblance to type I. Van Beneden (8) also found nematocysts in the 

 endoderm of some larval Cerianthidse, and gave many figures ; he distinguished two main 

 types of nematocysts, the first type closely resembling I, while the second comes near III, 

 but the thread is much shorter in Ovactis hrasiliensis (PL 3, figs. 2, 13, 14, 15). The 

 nematocysts consisting of three sorts from the " botrucnides " * and "cnidorages" 

 of Hensenanihula (Pis. 12, 14, 15) bear some resemblance to II, but the pointed 

 extremity of the "fil rectiligne " is directed towards the base of the nematocyst 

 (cp. PI. 12, figs. 13 and 14, with my PL 6, fig. 58 a, b), but one of these in the exploded 

 condition shows a long tapering thread. According to van Beneden each of these 

 nematocysts has a semilunar nucleus attached to it, the "fil rectiligne" being pre- 

 sumably protoplasmic, as may be inferred from the developmental stages (PL 12, 

 figs. 15—18). 



The respective functions of these types of nematocysts and the different ways in 

 which they are used can be ascertained only by means of actual experiments on living 

 polyps. Nos. I and III in all probability have a stinging function, which may account for 

 their mutually exclusive distribution, the latter restricted to the coils of the mesenterial 

 filaments, the former found mainly in the tentacular batteries. On the other hand, 

 type II may not have a stinging function ; in this connection it may be pointed out that 

 their sacs sometimes take a brownish tinge in iron hsematoxylin and eosin like the 

 mucous vacuoles. Could they then have an adhesive function and could that be the 

 reason why they are found interspersed among the nematocysts I in the terminal 

 tentacular batteries as well as among those of type III in the coils of the filaments 1 



In Gardiner's polyps of Coenopsammia nematocysts III f are present in the 

 convolutions of the mesenterial filaments, but the protoplasmic core has not been met 

 with in any of them. From Gardiner's description and figures it would appear that he 

 regarded these as the final stage in the development of type II. His " mesenterial 

 nematocyst" in fig. 14 is a reconstruction and a combination of types II and III, having 

 both the axis (" eversible portion") and the coiled thread. In a few cases I have seen 

 structures similar to fig. 15 which presumably belong to III, with the greater part of the 

 thread broken off. The appearance of a row of hairs may be due to the breaking of 

 the turns of the spiral surrounding the axial strand ; such a condition is presented by 

 some of the nematocysts III of my polyps of Favia favus (Forsk.) in which there is no 

 doubt whatever that the spiral round the axial strand has been broken at places. It is 

 also to be noted that while most of the authors cited above place the nucleus in the 

 protoplasm surrounding the nematocyst-capsule, Gardiner in his figs. 17 and 18 has 

 shown it inside the capsule. 



* " Botruonides " is the name given by van Beneden to certain curious endodermal structures having the 

 form of bunches of rounded grains which take the place of acontia in Cerianthula, Hensenanihula and 

 Calpanthula ; the individual grains which he has termed " Cnidorages " fall off into the gastro-vascular cavity 

 on attaining their full size. 



t Nematocysts II and III in Gardiner's polyps do not appear to have been well fixed. 



