366 SYDNEY J. HICKSON. 



water. They seem to swell considerably in dilute acetic acid, 

 so that some of the free nematocysts measured as much as 

 O'OIS mm. in length, but I do not think they are ever as large 

 as that in their natural position in the ectoderm. The filament 

 is long, easily broken, and is not provided, so far as I could 

 discover, with any barbs. 



In sections of preserved specimens the nematocysts are not 

 very easily observed, as they are usually shot and lost during 

 the process of killing the colony in an expanded condition ; but 

 they may be demonstrated by staining sections of colonies 

 killed contracted in spirit, or any other preservative, in eosin 

 and hsematoxylin. By this method the nematocysts are stained 

 blue and the ectoderm-cells pink. 



The extremely small size of the nematocysts of Alcyonium 

 is not by any means exceptional in the case of the Alcyonarians. 

 Moseley stated that in Sarcophyton there are no nematocysts, 

 and the late Professor Marshall and his brother (29) were un- 

 able to find them in Virgularia mirabilis. In Pennatulids 

 generally, according to Kolliker (24), they are exceedingly 

 minute, and their presence could not always be determined in 

 spirit specimens. 



Wilson (38) says that in the endodermic mesenterial filaments 

 of Paralcyonium there are " scattered irregularly through the 

 filaments minute nettle capsules. They are remarkable for their 

 very small size, being smaller than the nuclei of the endoderm- 

 cells. They have an oval form, and each contains a spirally 

 coiled filament. In the minuteness and rarity of the nettle 

 capsules the mesenterial filaments of the Alcyonaria differ from 

 those of the Actinians, and it seems possible that in the former 

 group they are to be regarded as rudimentary organs." 



The figure given by this author of the nematocysts of the 

 endodermic filaments on Paralcyonium is the only figure yet 

 published of the nematocysts of Alcyonarians. 



The Mesenterial filaments. — I have nothing new to add 

 to Wilson's excellent account of the structure of the dorsal 

 mesenterial filaments. 



The dorsal mesenterial filament consists of columnar ciliated 



