1915. | J. RitcHte : Hydroids of the Indian Museum. 563 
The simplest definite attachment is that of the larval hydroid 
of Gonionemus. Here there simply occurs at that surface of the 
planula-like bud which comes in contact with the substratum an 
increase in the thickness of the cells, so that the ectoderm of the 
base becomes a columnar epithelium. There seems to be no secre- 
tion of masses of mucus, but at any rate ‘‘it has now secured 
a firm hold upon the bottom, being so closely applied that it is 
quite hard to dislodge it’ (Perkins, 1903, p. 771). In the above 
sentence Perkins would seem to hint that the adhesion is physical. 
In Haleremita the attaching area has differentiated a stage further: 
for while it still consists of a simple layer of special elongated 
epithelium, there are associated with it many gland-cells which 
exude the secretion by means of which the polyp is attached to 
the substratum (Schaudinn, 1894, p. 228). 
A clear advance is marked by the condition of Hydra and 
Protohydra, for here a first organ of attachment, as distinct from 
a mere differentiation of ectodermal cells, is apparent. Neverthe- 
less this organ (the foot, pedal disc, disque pedieux, Fusscheibe, 
Fussplatte) retains the condition of elongate epithelium, with 
associated secretory cells the mucus of which acts as an accessory 
holdfast, but it is capable of grasping a firm surface and relin- 
quishing its hold at will. 
I regard as closely akin to the foot of Hydra in differentiation 
the “‘sucker-like’’ adhesive organs of the miniature adults of 
Myriothela cocksii (‘* phrygia’’), mentioned by Hardy (1891, p. 513) 
as remaining attached to the surface of the parent during develop- 
ment. 
Greater structural complexity is shown by the problematical 
‘* Basalscheibe’’ of the miniature-adult buds of Tiarella singularis 
minutely described by Schulze (1876, p. 412 and Taf. EN fis 2): 
In shape and minute structure this curious organ bears a striking 
resemblance to the naked basal disc observed in one young indivi- 
dual of Annulella with five tentacles, to the basal bulb of young 
specimens (see plate xxx, fig. 1) or to a section of an adult bulb 
(pl. xxxa, fig. 9). On account of these resemblances I have no 
hesitation in discarding Hartlaub’s suggestion that it may be 
“ein fur die pelagische Lebensweise wichtiges Organ’’ (Hartlaub, 
1903, p. 34), and regarding it is an attachment organ developed 
in preparation for the settling down of the pelagic phase. In 
exactly the same category may be placed the basal discs of M arge- 
lopsis stylostoma,' Margelopsis gibbesi, and Margelopsis haeckelii 
discussed by Hartlaub (1903, p. 34). 
Subsequent to fixation the flattened disc-like ‘‘ Fussplatte”’ 
of the adult Tvarella, with its coats of both dark and amorphous 
perisarc, continuous with those of the hydrocaulus, seems to have 
degenerated from the larval state as regards cellular distinctive- 
ness. 
' A designation which since it indicates simply a young phase of 7zarella 
singularis, must lapse (see Bedot 1911, Peni): 
