STINGING-CELLS IN CUASPEDOTE MEDUSAE. 765 



Medusae, I have endeavoured in this paper to give as complete 

 an account as possible of the origin and distribution of the 

 nematocysts of this form. 



The material used for this investigation was collected by 

 Dr. Cunnington and myself in Lake Qurun, and was carefully 

 fixed either with osmic acid or with hot corrosive sublimate. 

 Sections were cut by the ordinary paraffin method and a 

 number of stains were tried, the best results being obtained 

 with hosmatoxylin followed by eosin ; this produced an 

 excellent double-stained effect, the eosin bringing out the 

 nematocysts and rendering them most conspicuous. Borax 

 carmine followed by picro-indigo-carmine was another good 

 differential stain and iron-htematoxylin was useful when 

 examining sections of the developing Medusae. The work in 

 connection Avith this paper was carried out partly in the 

 Morphological Laboratory at Cambridge and partly in the 

 Zoological Laboratory of Birmingham University. I wish to 

 express here my sincere thanks to Professor F. W. Gamble, 

 who very kindly read through my manuscript and made 

 many valuable suggestions, 



2. The Stinging-cells op the Adult Medusa op MffiRisiA. 



As mentioned above, a striking feature of the anatomy of 

 this medusa is the presence of numerous thread-cells^ in the 

 endoderm at the base of the manubrium. At first it seemed 

 possible to account for their occurrence in this unusual 

 position by assuming that these stinging- capsules were used 

 ones taken in by the jelly-fish together with its food. On 

 careful consideration this view was found to be quite un- 

 tenable, for — 



' The nomenclature of the different parts of the stinging-cells is 

 somewhat ciimbrons and complicated ; moreover, the various names 

 have been used very loosely. In this paj)er I have employed the terms 

 thread- cell or stinging -cell for the whole structure comprising the 

 nematocyst (the actual stinging capsule), and nemato blast (the 

 cell in which the former is embedded, and of which the cnidocil and the 

 stalk are parts). 



