8 THE VOYAGE OF H.M.S. CHALLENGER. 



an open orifice which is usually very oblique. In some very rare cases (PL VIII. figs. 

 4-7, and PI. XIX. figs. 1-3) the lateral nematophores are absent. 



In a singular and beautiful species [AcantJiodadium huxleyi, PI. IX.) contained 

 in the Challenger collection, the hydrocladia become towards the dorsal extremities of the 

 branches atrophied, lose their hydrothecse, and are converted into spine-like appendages, 

 which carry from base to apex two longitudinal alternate series of minute cup-shaped 

 nematophores (PI. XX. fig. 3). 



b. CauUne nematophores. — These are usually small, cup-shaped bodies, situated on 

 various parts of the hydrocaulus, with the cavity of which they communicate. They are 

 generally disposed in linear series (PI. XVII.) on the main stem and principal branches, 

 and often form definite symmetrical groups of two at the points where the hydrocladia 

 spring from the stem. Though quite difi"erent from the moveable nematophores of the 

 Eleutheroplea, — being seated on a wide base which fixes them to the stem, — they would 

 seem to be in many cases easily detached. 



c. Gonosomal nematophores. — The system of nematophores attains in the gonosome 

 of the Phylactocarpal Statoplea a remarkable development. The characteristic denticles 

 which are found on the margins of the leaflets, which combine to form the walls of the 

 corbula (Pis. XL and XII.) in Aglaophenia, are only slightly modified nematophores. 

 These denticles are tubular with a terminal orifice, and their cavity is in communication 

 with that of the leaflet, while this opens into the common basal rachis of the corbula. 

 In most cases a nematophore is specially developed at the base of each leaflet in the form 

 of a spur. In one remarkable form (PI. XX. fig. 6) branching chitinous ridges are 

 developed on the walls of the corbula, and enclose cup-shaped nematophores in bifurcations 

 of their branches. 



But nematophores are largely developed not only in the corbula, but in the other 

 forms of Phylactocarp, where they constitute a very characteristic feature. They occur in 

 such cases along the branches of the Phylactocarp, or along the common basal rachis, and 

 are usually present in the form of denticles or cup-shaped bodies, arranged in two opposite 

 or alternate series. In Lytocarpus spectahilis (PI. XV.) they are in the form of a pair 

 of stout opposite spines on every internode of the phylactocarpal rachis, and are each 

 provided with a terminal aperture and also with a lateral aperture close to the base 

 (fig. 5). In Lytocarpus racemifera (PL XIII.) there is, in addition to the pan: of 

 opposite spine-like nematophores on each internode, an azygous spine on the front of 

 the internode (figs. 4-6). A similar azygous spine-like nematophore is in Lyto- 

 carpus spectahilis carried by that internode of the rachis which supports a gonangium 

 (fig. 2, p. 44). 



