36 Mr. R. Vallentin on the 



central nervous system in Melicerta ringens. He says : — 

 *' Sur la face dorsale du pharynx, immddiatement an-dessus dc 

 I'amas glandulaire dependant du systbme excr^teur, se voient 

 deux ou quatre cellules transparentes qui occupent pr^cise- 

 ment la position oti I'on a decrit le ganglion cliez tous les 

 Rotateurs oil il a etd vu. Elles sont pourvues d'un noyau 

 volumineux qui leur donne beaucoup l'aj)parance d'une 

 cellule nerveuse et deux d'entre elles envoient un filet a 

 I'organe tactile impair." 



1 have placed in my illustrations a section taken through 

 the middle of the brain and surrounding parts of M. comfera. 

 I have selected this Rotifer mainly on account of its size and 

 the ease with which one can see the nerve-cells. In ;!/. 

 ringens the brain is, as stated by M. Joliet, small, the nerve- 

 cells being not nearly so numerous as in M. comfera [vide 

 PL IV. figs. 2-4 and the accompanying explanations) . 



Lacinularia socialis. (PI. V. figs. 9-13.) 



Dr. Hudson in his monograph gives a summary of our 

 present knowledge concerning the nervous system of this 

 species. He says [loc. cit.), " Prof. Huxley describes and 

 figures a ciliated cup beneath the chin, just as in M. ringens ; 

 and below this cup, underneath the surface on the ventral side 

 ' a bilobed homogeneous mass resembling in appearance the 

 ganglion of Brachionus.^ Tiiis organ he supposes to be the 

 true nervous ganglion. Dr. Leydig, on the other hand, 

 points out two nucleated polar cells, giving off threads, just 

 below the mastax, and two similar ones at the junction of tlie 

 foot and trunk." 



According to my observations I find a group of nerve-cells 

 placed immediately beneath the transverse band which con- 

 nects above the mouth the paired lateral excretory tubes [vide 

 PL V. fig. 12). This group of cells consists of unipolar gan- 

 glion-cells. On reference to fig. 12 and the accompanying- 

 explanation it will be further noticed that from the dorsal 

 edge of this nervous mass nerve-fibres are given off which 

 ultimately terminate in one of those large cells placed at 

 regular intervals along the inner edge of the corona, and 

 classed under the head of " vacuolar thickenings " by Prof. 

 Huxley (3). 



Prof. Huxley says concerning these " vacuolar thickenings " 

 as follows : — ^' . . . the thickenings in the trochal disk are 

 mostly towards its lower surface and at its inferior margin; they 

 are generally four or five on each side, and are connected by 

 branched filaments with that body on each side of the pharyn- 



