118 THE POTIFEPA. 



Family V. MICKOCODIDJI. 



Corona obliquely transverse, flat, circular ; buccal orifice central ; ciliary wreath 

 a marginal continuous curve encircling the corona, and two curves of larger cilia, one on 

 each side of the buccal orifice ; trophi forcipate ; foot stylate. 



Genus MICROCODON, Ehrenberg. 

 GEN. CH. Eye single, centrally placed , just beloiu the ccrona. 



M. clavus, Ehrenberg. 

 (PL XL fig. 1.) 



Microcodon clavus . . Ehrenberg, Die Infus. 1838, p. 395, Taf. xliv. fig. 1. 



„ „ . . Pritchard, Infusoria, 1861, p. 665, pi. xxxii. figs. 371-2. 



„ . Grenacher, Sie&. u. Kull.Zeits.Bd.xix. 1869, p. 487, Taf. xxxvii. fig. 2. 



This curious Kotiferon, for which, though the only species of the genus, it has 

 been found necessary to make a new family, was discovered by Ehrenberg in 1830. It 

 has since been described by Dr. Max Perty and Dr. H. Grenadier (loc. cit.), and has 

 been found in England several times by Dr. Collins, at Sandhurst, and lately by Miss 

 Davies, at Woolston. It has, however, escaped the notice of the majority of observers 

 during the last fifty years, in some measure no doubt owing to its small size ; for 

 though its whole length is T A ft inch, more than one-half of this is taken up by a long 

 narrow foot, so that the actual body of the animal does not much exceed ^i-g- inch. 

 Ehrenberg placed it in his family Megalotrochcea ; but neither in its ciliary wreath, its 

 trophi, nor its foot, does it resemble the Iihizota. The corona is a flat circular disk, set 

 obliquely on the trunk, and with its dorsal edge pointing forwards. 1 A complete ring of 

 minute cilia edges the disk, and these perform the office of driving the food to the buccal 

 funnel. The entrance to this latter is near the centre of the corona, a little towards the 

 ventral surface. It lies between two curves of large unequal cilia, of such lengths and 

 so arranged that they form on each side an oval border to the buccal orifice. Usually 

 these large cilia are at rest ; and Microcodon, under the action of the smaller cilia, either 

 glides along swiftly or oscillates gently to and fro over the same spot, as if it were moored 

 by a thread from its single toe. It is possible that this curious hovering over one place 

 may be due to the mutually opposing action of the minute cilia of the two halves of the 

 corona, but it always gave me the impression that the animal was at these times moored 

 by a viscous thread to some spot on the glass. Every now and then, whether gliding 

 along or hovering, the creature darts suddenly forward with the utmost swiftness, accom- 

 plishing this by vigorous strokes from the two rows of larger cilia. It would seem that 

 it has unusual control over this apparatus, for Dr. Grenadier has seen, in an injured 

 specimen, these inner cilia lifted and depressed one by one ; and has traced to them 

 what he supposes to be nerve-threads arising from the depth of the corona. A further 

 peculiarity noticed by this observer is that the corona remains expanded, no matter how 

 the animal be treated. 



The trophi (fig. lc) consist mainly of two ribbed rami, attached to a long narrow 

 plate (the fulcrum), which is seen edgewise in the figure. I think, too, that I detected 

 delicate pointed unci on each side of the incus. The whole are included in a long conical 

 inastax, closely resembling that of Polyarthra, and pointing downwards towards the 



1 Ehrenberg says that its shape is that of a transverse figure 8 ; but Dr. Grenacher, Dr. Collins, 

 Mr. Gosse, and myself all agree that it is circular. Mr. Gosse, however, points out that, when the 

 corona is inclined to the line of sight, it does look somewhat like that of a Limnias. 



