OF THE ROTATCRIA. 435 



portions of tissue fixed on by him as nervous masses, receive in general an 

 entii^ely different intei-pretation. Thus in the case of Lachmlaria the sup- 

 posed 4-6-lobed brain, with extending nerve-fibres, is set down as mere col- 

 lections of " vacuolar tliickenings," with intercuiTent fibres of connective 

 tissue. The same inteipretation is extended to the " nine pairs of ganglia, 

 with fine interlacing nerve fibres," in Notommata clavulata, and to the four 

 or five such in Diglena laciistris ; yet in both these species, the central or 

 brain ganglion represented by Ehrenberg is allowed to retain this character 

 by Leydig, who sets aside all the rest as mythical. 



The following critique on Ehrenberg's views is fi'om Prof. Williamson : — 

 " The small organs so common amongst the Eotifera, and which Ehrenberg 

 regards as nen'ous ganglia, are abundant in the MeJkerta, but they aff'ord no 

 coimtenance to the hj^^othesis of the great Prussian Professor (XXXVII. 

 17 h). They appear to be nothing more than small ceEs, or vesicles, formed 

 of granular viscid protoplasm, very similar to those into which the yelk of the 

 eg^ becomes di\'ided. Sometimes the}^ float freely in the fluid which distends 

 the integument and bathes the viscera ; at others, thin ductile threads pass 

 from one vesicle to another .... There is no uniformity in their arrangement 

 in different individuals. They diff'er as widely as possible in their size, 

 number, and distribution. So far fi'om being nervous vesicles, they appear 

 rather to be cells modified into a rudimentary foiTQ of areolar (connective) 

 tissue. That they are hollow vesicles or cells, very viscous, readily cohering, 

 and, o^^g to this coherence, readily drawn out by the movements of the 

 various organs to which they are attached, are facts capable of easy demon- 

 stration." 



A central nervous mass or brain, immediately subjacent to the eye-specks, 

 and above the oesophagus or pharynx, which sends off nerve-fibres in different 

 directions, is, as already intimated, generally admitted to exist. It is men- 

 tioned by Siebold, Perty, Gosse, Dabymple, Leydig, Cohn, and others. The 

 two first-named authors allude to it as a group of ganglions ; but Leydig 

 affirms that, although it may be lobed, it is always a single and undivided 

 organ. Some, again, have treated of it as forming a loop or ring around the 

 gullet ; but such a condition is denied by Leydig, who states that it only 

 extends itself in the form of diverging nerves, which end by enlarged extre- 

 mities, and never form loops, such as Ehrenberg represented, around the 

 tubular process or respiratory siphon. 



This nervous centre or brain, supporting the eyes, is seen in the families 

 Hydathum, Euclilanidota, and Brachioncea. Leydig, however, cannot admit 

 the masses supposed to represent the cerebrum in the families GEcistina, Mega- 

 lotrochcea, and Fhscidaria, nor the pairs of nerve-hke ganglions at the base 

 of the trochal disk of Stephanoceros, to have a cerebral character ; he supposes 

 them rather to be " coils of the respiratoiy canal, or heaps of granules or 

 nuclei, such as are met with beneath the cuticle." 



Prof. Huxley discovers the nervous centre under a peculiar and unusual 

 usual form in Lacinularia socialis. To quote his words — " On the oral 

 side of the neck of the animal, or rather, upon the under surface of 

 the trochal disk, just where it joins the neck, and therefore behind and 

 below the mouth, there is a small hemispherical cavity (about y^i^j^th of 

 an inch in diameter), which seems to have a thickened wall, and is richly 

 cihated within. Below this sac, but iu contact with it by its upper edge, is 

 a bilobed homogeneous mass (about -g-l-jyth of an inch in diameter), resembling 

 in appearance the ganglion of Bmchionus, and running into two prolongations 

 below ; but whether these were continued into cords, or not, I could not make 

 out. 



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