Anatomy of certain Rotifers. 37 



gcal mass in which the band of the water-vascular system 

 terminates." In this species of Rotifer tactile organs have 

 never been observed ; I take these " vacuolar thickenings " 

 to be nerve sense-cells and to perform the function of tactile 

 organs. Occupying the position they do, on any foreign body 

 coming into contact with tlie expanded edge of the corona 

 the stimulus would be immediately conveyed through these 

 marginal sense-bodies along the nerves and so to the brain. 

 There is, however, a very close connexion between the mar- 

 ginal sense-cell and the dilated portion of each lateral canal 

 in the corona. I have, however, satisfied myself that the 

 nerve-fibre in each instance runs over the dilated portion of 

 the lateral canal and so joins the brain. Be this as it may, 

 cells similar in structure but not showing any connexion with 

 the central nervous mass are also visible in the trochal disk 

 of Melicerta ringens, M. comfera, and Brachionus 7'ubens. 



Attention may here be directed to a group of cells placed 

 in the region of the anterior third of the foot. Dr. Leydig (4) 

 gives a very exact representation of these cells as seen in 

 optical section. From a close scrutiny of Dr. Leydig's figure 

 one would be inclined to imagine that these cells were placed 

 immediately beneath the cuticle of the animal. Serial sec- 

 tions, however, show these cells to be grouped together in the 

 central space (body-cavity) of the foot, the longitudinal 

 muscles with the mucous cells forming a complete wall round 

 them {vide PI. V. fig. 9). Each cell is seen to be oval in 

 outline and possessing a nucleus and nucleolus. ^ Anteriorly 

 and posteriorly from each cell processes are given off, the 

 processes from the anterior region of each cell being lost in 

 the viscera, while posteriorly they appear to unite with the 

 muscles forming the attached extremity. These processes 

 are so extremely fine as to render it difficult for one to trace 

 them to their destination. Dr. Leydig takes these cells to 

 be nervous in function. Dr. Hudson {loc. cit.), after giving 

 a summary of the researches of previous investigators con- 

 cerning the position of the known nervous centres in other 

 Rotifers, seriously questions Dr. Leydig's statement con- 

 cerning the function of the cells in question. At present I 

 think we must own we are unable to offer any satisfactory 

 explanation concerning their function. 



Muscular System. 



Melicerta ringens and M. conifera. 

 (PI. IV. figs. 1-8.) 



So far as I can discover there is no difference in the 



