354 DESCRIPTION OF [Rotatoria. 



glands open into a contractile vesicle for fructification. 

 The vascular system and gills are observed in H. senta. 

 In both species the central ganglia, with its cervical 

 thread or loop, is visible. 



582. H YDATINA senta ( Vorticel/a senia, M.) The large 

 Hydatina. Body conical, hyaline ; margin of the rotatory 

 organ ciliated ; foot truncated and robust. The vibratile 

 organ, when extended, is always in motion ; it consists of a 

 simple external wreath of cilii, somewhat interrupted at 

 the mouth, and eleven internal bundles of cilii, each en- 

 veloped in a muscular sheath. The body has nine 

 muscular bands thus situated; one upper or anterior dorsal 

 muscle (no under or posterior one), two anterior ventral, 

 and two posterior ones closing thereon ; one right, and one 

 left anterior lateral, with posterior ones in continuation. The 

 five anterior muscles arise between the muscular bundles 

 of the rotatory organ, mostly at the margin ; the dorsal 

 ones arise from the centre, near the central ganglion, and 

 are collectively attached to the internal skin of the abdomen, 

 between the fourth and fifth transverse vessels, their in- 

 serted extremities being enlarged. Here the four posterior 

 muscles arise, and are inserted where the pincer-like foot 

 projects ; two longitudinally-striated muscular sheaths en- 

 case the inner root of the divided foot; and there is a 

 sphincter to the anal opening. The fibrous structure of 

 the band-like longitudinal muscles, as sometimes also 

 transverse corrugations of the fibres, are as distinct as in 

 the larger animals. During the contraction of the body, 

 they become shorter and broader, by which they are easily 

 distinguished from the other band-like and filiform organs, 

 which only become curved during contraction of the body 



