THE ROTIFEKA. 



T. LONGISETA, Ehroibcrg. 

 (PI. XIII. fig. 6.) 



Triarthra longiseta . . . Ehrenberg, Die Infus. 1838, p. 447, Taf. Iv. fig. 7. 

 ... Hudson, Mon. Micr. J. vol. i. 1869, p. 176, pi. vi. 



... Grenacher, Sieb. u. Koll. Zeits. Bd. xix. 1869, p. 491, Taf. 



xxx vii. fig. 3. 



SP. CH. Body oval; buccal orifice prominent but not beaked, cup-sJiaped; spines 

 more than twice the length of the body ; eyes wide apart; oesophagus long. 



The habit of this interesting creature is to swim slowly forward while turning round 

 its longer axis, and every now and then to dart out of its course by jerking forwards the 

 three long spines which usually trail behind it. The corona is oval, and bears in its 

 centre one broad, low prominence, with a smaller one on either side of it ; and just within 

 each of these latter is placed a red eye. The buccal orifice is cup-shaped and has its 

 inner surface lined with cilia. The buccal funnel slopes backwards and upwards towards 

 the dorsal surface to meet the mastax, whose trophi are almost identical with those of 

 Melicerta ringens. The asophagus is long and narrow, and the stomach and intestine 

 are usually separated by a deep constriction. The gastric glands (fig. 6a) are curiously 

 shaped, and frequently studded with what appear to be oil-globules. The vascular 

 system is delicately transparent, and difficult to be seen. I have traced the lateral canals 

 on each side, for some distance down the trunk, from a plexus of tubes in the neck, and 

 have detected just there a vibratile tag. I failed to discover the contractile vesicle, but 

 Dr. Grenacher (loc. cit.} has seen it, in its usual position, close to the cloaca. There is a 

 large ovary ; and the newly laid eggs remain attached to the parent by a thread for some 

 time after their exclusion. The ephippial eggs (fig. (>/) are as curious in shape as the 

 gastric glands, and are protected by a thick layer of yellowish transparent cells. By 

 bringing into focus the central inner portion of the head, seen sidewise, a bluish and 

 roughly rhomboidal mass may be observed ; this is the nervous ganglion, and above it 

 are the eyes, and from it threads extend to a setigerous fossa in the neck, as well as to 

 rocket-headed antennae, one on each side (fig. 6e) just under the surface. Each eye 

 (fig. 6b) is a clear, colourless, refracting sphere -j^Vo mcu m diameter, resting on, and 

 partly imbedded in, a flat plate of red pigment. The longitudinal muscles are very 

 powerful, and are strongly striated ; the strict not being straight transverse lines, but 

 irregular obliquely transverse curves (fig. Gc). Indeed they appeared to me to alter both 

 in direction and in size as I looked at them, giving me the impression that I was looking 

 at illusory stria, produced possibly by looking through separated sheets of striated fibre, 

 lying over each other. There is an unusually powerful muscular collar running round 

 the neck. The spines are stiff quill-like appendages, broadest at their attached bases, 

 and tapering at their free ends. The bases (fig. 6d) are like quills that have been 

 obliquely cut across, and it is by these cut surfaces that they are attached, one on each 

 side of the corona, just above the neck ; and one on the ventral surface, at the spot from 

 which the foot springs, in those Eotifera that possess one. The spines are notched hero 

 and there (fig. GtZ), and finely imbricated towards their tips. On looking at fig. 6, it will 

 be evident that if the muscular collar round the neck be suddenly contracted, and the 

 head withdrawn, the spines will be first dragged across the stiff edge of the trunk, 

 below the collar, and then jerked forward by the downward pull of the head. 



How the third spine is moved is not so clear. Dr. Grenacher suggests that it is 

 dragged forward by the other two, which are often crossed beneath it ; but adds that 

 this is a forced explanation. It is probable, I think, that this spine is driven forward 

 by the sudden jerk downwards on its base, when the longitudinal muscles sharply com- 

 press the stiff ventral cuticle. Fine muscular fibres surround the trunk at regular 



