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



begin at a little distance from tlie margin of the pedal disk, become less distinct as they 

 ran upwards, and disappear towards the margin of the peristome. Besides the furrows 

 the body is covered with numerous small papillte, which can only be distinctly recog- 

 nised with the magnifying glass, and which show a pattern like shagreen on the wall, as 

 they are all of the same size and closely compacted. The entrance to the oral disk is 

 surrounded by a circular swelling projecting above the surface, which belongs to the 

 upper end of the wall ; a shallow circular furrow runs near the lower end at a short 

 distance from the margin of the pedal disk. 



Nothing further could be observed in the uninjured animal, and on account of its 

 smallness and strong contraction no further results could be expected from a dissection 

 with scissors and knife. I therefore cut out a piece about the size of a quadrant, in which 

 I examined the circular muscle, the oral disk, the tentacles, the oesophagus, and the septa 

 in transverse sections, changing the plane of the section as occasion required. 



The circular muscle, which lies in the mesoderm, is so powerful in Tealklium that the 

 bulk of it has not room enough in the thickness of the wall. Just as a purely endodermal 

 circular muscle causes a circular swelling on the inside, so this strong mesodermal muscle 

 causes a similar swelling on the outside, as the surface of the wall is arched out to 

 nearly four times the usual thickness ; it can be recognised by simply looking at the 

 animal, and has already been briefly mentioned. It probably becomes still more apparent 

 when the Tealidmm is extended, and then produces a girdle under the origins of the 

 tentacles, on account of which I have named the form Tealidium cingulatum (PL VI. fig. 2). 

 The entire mass of the muscle is club-shaped in transverse section. The smaller end, 

 which is turned downwards, runs out into a fine point, which extends nearly to the endo- 

 derm, through the broad intermediate layer of connective substance. 



The separate muscular fibres are fine, and so are the primitive bundles formed by 

 them ; from the manner in which the latter are grouped, it seems probable that they arise 

 from division of larger bundles, of which a few still remain (PL VIII. fig. 8). The 

 process of division seems to go on very rapidly in the peripheral parts, as we there find 

 not only groups of two, three, and four fibrillse enclosed in the fibrous connective 

 substance, but very frequently completely isolated single fibrUlse (PL VIII. fig. 7). 



There was nothing remarkable about the oral disk and the tentacles ; their radial 

 longitudinal muscular fibres are ectodermal, and extend in an almost smooth layer, which 

 is only distinctly pleated at the bases of the tentacles. The number of the tentacles 

 which are distributed in two circles amounts to twenty-four ; they are of no great length, 

 so that they are completely hidden under the contracting circular muscle. 



The number of the septa in the quadrant examined amounted to seven ; as they usually 

 correspond to the longitudinal furrows already mentioned, their number in the entire 

 animal must be reckoned at more than twenty. Their paired arrangement is- shown by the 

 course of the miiscles ; two directive septa were present in the quadrant, so that there is no 



