INTRODUCTION. XV11 



Simple cup-shaped nematophores occur on Plumularia 

 pinnata, while those of P. sttacea and some other species 

 of this genus and of Antennularia are bithalamic. 



The nematophores occur on various parts of the 

 zoophyte, and are usually present in force about the 

 hydrotheca. They are met with over all portions of the 

 stem and on the creeping fibre ; but the most remarkable 

 aggregation of them is found on the corbula, or case that 

 protects the gonophores in the genus Aglaophenia, where 

 every tooth on the crested ribs is formed by one of these 

 curious bodies*. 



The contents of the nematophore have been recently 

 investigated by Prof. Airman f; and to him we owe the 

 important observation that the soft granular mass which 

 fills it "has the power of emitting very extensile and 

 mutable processes," that comport themselves in every 

 respect like the pseudopodia of an Amoeba, which they also 

 resemble in their structure. These processes " consist of 

 a finely granular substance, which undergoes perpetual 

 change of form;" and "they can be entirely withdrawn, 

 so as to leave no apparent trace of their existence" J. 

 (Woodcut, fig. vi.) 



* Prof. Huxley, in a paper " On the Anatomy and Affinities of the Family 

 of the Medustu " (Phil. Trans. 1849, p. 427), in which, I believe, we have the 

 first notice of the nematophore, has described a form occurring in a foreign 

 species of Plumularia as consisting " of a stem proceeding from the pedicle 

 of the ovary, bearing a series of conical bodies.' 1 This evidently corresponds 

 with the spur-like process fonnd at the base of the corbula in our own 

 Aglaophenia fubulifera, nnd is nothing more or less than a supernumerary 

 rib or "leaflet," edged, as all the elements of the corbula arc, with 

 nematophores. 



t "On the Occurrence of Anicebiform Protoplasm, and the Emission <,(' 

 !'-"ii<lopodui, among the Hydroida,'' Ann. N. H. for March 1XIV1. 



\ The substance of the body amongst (he ITydroida really differs but 

 slightly from that, of the Protozoa. True it is differentiated into distinct 



b 



