NOTOMMATADJE. 41 



F. FORFICULA, Ehrenberg. 

 (PL XX. fig. 1.) 



Furcularia forficula . . . Ehrenberg, Die Infus. 1838, p. 421, Taf. xlviii. fig. 5. 

 ,, ... Gosse, Ann. Nat. Hist. 2 Ser. vol. viii. 1851, p. 199. 



... Lord, Micr. News, 1884, p. 235, fig. 27. 



[SP. CH. Body stout, straight, nearly cylindrical; broadest at the head, which 

 comes to a frontal point, where is a single red eye ; toes two, furcate, blade-shaped, 

 acute, decurved, the ventral edge of each notched with two strong teeth. 



The deep sickle-shaped toes, having their under-edges notched near the base, readily 

 identify this. 1 Its form is nearly cylindrical, slightly thicker in front ; the back is 

 sometimes gibbous, viewed laterally. The head forms a short regular cone, whose base 

 is the width of the head, at the apex of which is placed the small but distinct red eye. 

 The whole front appears set with cilia, which cause two vortices : a turbid occipital 

 brain is visible, carrying the eye at its anterior extremity. In contact with this as 

 usual, is an ample sub-globose mastax, with characteristic trophi. A long oesophagus 

 leads to the alimentary canal, which has thick granular walls, and bears two large 

 gastric glands. At times the dorsal portion of the stomach is inflated into a large 

 clear bladder, which displaces the granular walls around it. As this often appears and 

 vanishes rather suddenly, it has a singular effect. Towards the hinder part the granu- 

 lation becomes less opaque ; but whether there is any division between stomach and 

 intestine has not been clearly seen. A small contractile vesicle lies around the base of 

 the foot, and I have sometimes been able to trace the lateral canals and vibratile 

 tags. A small oblong or cord-like ovary generally occupies the venter, sometimes 

 dilated into a maturing granulate ovum. Many longitudinal muscles are visible, but 

 the contractions and contortions of the animal are so incessant as to render it almost 

 impossible to define them. By these contortions the firm skin is thrown into various 

 irregular angular folds. The foot seems composed of two joints, of which the basal is 

 by much the stouter, each enclosing a gland. The curved broad blade-like toes bend 

 downward at their sharp points ; each is cut into a strong projecting sharp tooth at 

 its base, and its foot joint immediately preceding has two teeth exactly similar. 



Ehrenberg alludes to this animal as very rare. I have been familiar with it for more 

 than five-and-thirty years, and I consider it by no means uncommon. I used to meet 

 with it in the waters around London, and have since found it in very many localities, 

 often among conferva, and in the floccose sediment of ditches. In confinement it is 

 often most restless, constantly swimming about with a swift gliding shooting motion, 

 and throwing itself into frequent folds and twistings. The body is nearly colourless, 

 but for the opacity of the granulate viscera, which appear white by reflected light. 



On repeated occasions I have observed, in this species, the curious habits already 

 referred to of inhabiting tubes, for some unimaginable purpose, of its own ingenious 

 manufacture. 1 cite the following note from my Journal, jotted down while under my 

 eye. " A fine specimen I found tenanting a long curved passage, in the yellow-brown 

 floccose from the ditch in Button Park. This was just wide enough to allow it to move 

 freely, and to turn its soft flexible body, when needed. It was about twenty times the 

 animal's length, outwardly undefined, being but a cavity formed in the irregular mass 

 of accumulated floccose. Within this, semi-transparent in parts, the Furcularia was 

 diligently pushing its way from end to end, turning back on itself the instant the end was 

 reached, not showing its nose out in the clear for a moment, and returning on its course ; 

 moving with considerable rapidity, never deviating and never resting. But after doing 

 this a long while, perhaps an hour or two, it began to pause here and there, and to move 



1 Ehrenberg describes and figures a species, Distemma forficula, of which I know nothing more, 

 with toes closely resembling the above. Only, to judge from his figs., the toes are recurved instead of 

 decurved, and the notching is on the dorsal instead of the ventral edge. 



