386 Rev. T. Hincks on the History of the Hydroida. 



of tlieir precise function. Meneghini seems to have been the 

 first to notice them ; he was followed by Huxley (1849) ; and 

 a few years later Busk gave a more complete and accurate 

 account of them, and drew special attention to the important 

 characters which they yield to the systematist. Allman (1864) 

 studied the contents of the nematophore, and established the 

 very interesting fact that the soft granular mass contained in 

 it has the power of emitting extensile processes, very similar in 

 structure and behaviour to the " pseudopodia " of an Amoeba. 

 More recently (1872) Kirchenpauer has minutely described the 

 varieties of nematophore which occur in the different groups 

 of Plumulariidffi, and has applied the results of his research in 

 a revised arrangement of the family*. After all, however, one 

 or two points have escaped observation which are worthy of 

 record. 



The presence of thread-cells in the protoplasm of the nema- 

 tophore has been noticed by Busk and Allman. They seem 

 not to occur universally; at least the latter observer failed 

 to detect them in Antennulmna antenmna, Linn. In all the 

 species which I have examined they are present, and occupy 

 the same position. 



It has been observed that these thread-cells are never carried 

 out in the " pseudopodia " — a remark which indicates that the 

 true structm-e of the protoplasmic offshoot enclosed in the chi- 

 tinous case of the nematophore has not been determined. In 

 all the cases that have come under my notice the terminal 

 portion of the sarcode-mass was divided into two distinct and 

 constant lobes, in one of which (the superior) the cluster of 

 thread-cells was immersed, while from the other (the inferior) 

 originated the extensile process. 



In the nematophores which stand out on each side of the 

 calycle in Aglaophenia pluma this bipartite structure may be 

 studied to great advantage. The superior lobe (PL XX. 

 fig. l,a) is elongate in form, and extends from about the 

 middle of the cavity to the outer extremity of the terminal 

 aperture ; it contains a number of rather large thread-cells, 

 arranged longitudinally at the very summit. The inferior 

 lobe, which originates at the base of the other, presents a 

 rounded outline (PI. XX. fig. 1, h) when at rest, and is com- 

 posed of a simple granular substance. 



In Plumularia setacea (PI. XX, fig. 2) the bilobate character 

 is equally marked, though, from the nature of the chitinous cup 

 or bowl in which the nematophore terminates, the two lobes 

 are more nearly on a level than in the previous species. At 



* ' Ueber die Iljdroidenfamilie Plumularidfe, einzelne Gnippen der- 

 selben imd ihre Fruchtbehalter.' Hamburg, 1872. 



