278 THE VOYAGE OF H.M.S. CHALLENGEK. 



diflferent regions of one stock. In PL LXXII. fig. 4 I have represented a fragment of a 

 specially elongated tubular system. This was trawled to the west of Manila (Station 207, 

 lat. 12° 21' N., long. 122° 15' E.) from a depth of 700 fathoms and a blue mud ground, 

 while in contrast to this the specimen trawled in the Bay of Sagami by Dr. Doderlein, 

 from about 150 fathoms and a clay bottom (PI. LXXI. fig. 2), exhibited quite short 

 tubular branches of at most 1 cm. in length. In the largest specimen of this lot, 

 which is figured in PI. LXXII. fig. 1, the tubes have a length of only 1"5 to 2 cm. 



In the spirit specimens, in which the whole soft tissue remains perfectly intact 

 with the dermal and gastral membrane, both the external and the inner surface are 

 uniformly marked by fine dark points arranged in transverse and longitudinal rows 

 crossing at right angles (PI. LXXI. fig. 2). Where the soft tissue has been removed by 

 maceration or by mechanical means, the beautiful quadratic network of the dictyonal 

 framework is more or less distinctly seen (PI. LXXII. figs. 1, 3). 



The diameter of the tubes increases continuously from the simple basal portion to the 

 freely projecting, widely open, terminal cups. On quite young specimens only a few 

 centimetres in height, the stalk measures hardly 3 mm. in breadth, just above the plate 

 of attachment, while in older specimens external thickening results in a transverse 

 diameter of 5 to 10 mm. While the cup-shaped ends of the tubes in young specimens 

 have usually a width of only 5 mm. or so, the terminal openings of the large stocks are 

 frequently 15 to 20 mm. in diameter. 



Since the dichotomous ramification begins at a very early stage at variably distant 

 intervals and not in the same plane, but in planes often disposed at right angles to one 

 another, no long straight main trunk results, but an irregular much twisted system of 

 tubes, expanding on all sides. The anastomosis seems to occur partly as the result of 

 direct union between newly formed tubes which meet one another in their growth, and 

 partly as the result of the apposition of adjacent tubes which are at first externally united, 

 and afterwards come into direct communication by the absorption of the intervening 

 partition. Now and then, but on the whole rarely, I have observed one or other of the 

 tubes, bent downwards or to the side, and closed by a transverse porous plate, while all 

 the others remained open. I can only regard such a closure as an abnormality, which 

 has probably resulted as a protection against the injurious influence of mud or the like. 



In regard to the microscopic structure of the dictyonal framework, I have in the first 

 place to notice, in opposition to the previous statements of other investigators, that the 

 greater part of the whole tubular system, and especially the superior youngest portion, is 

 supported by a single-layered network, but that in the lower, and therefore older 

 portions, and also at the base of all the stocks which are not very young, the framework 

 exhibits two la3-ers or more (PI. LXXIII. fig. 2 ; PI. LXXVI. fig. 3). The network en- 

 closes approximately cubical meshes. This many-layered framework has undoubtedly 

 arisen in this way, that to each distal ray of the single-layered lattice-work the proximal 



