or THE KOTATOEIA. 437 



Mr. Dalrymple mentions the presence, in liis Notomuiata anylica, of a small 

 ganglion sending off nerves to the stomach, salivary glands, and ovary ; but 

 Leydig looks upon this structiu-e as no more than the cells and fibres of con- 

 nective tissue, and states that "■ similar clear cells, of various size, having 

 dehcate elongated branches, are seen in Notommata centriira, N. Mi/nneleo, 

 N. davulata, and in Diylena lacustns. The delicate branches, or threads, 

 extend between the epidermis and the viscera of the body, and were described 

 by Ehrenberg to be nerves, but are actually the means of retaining the vis- 

 cera in situ,'^ — a conclusion supporting that of Prof. Williamson. 



There is, however, one set of nerves recognized by most observers, which 

 proced from the cerebral ganglion to the surface of the body, ending at the 

 bottom of the epidermic pits described above (p. 408), from which stiff cilia or 

 bristles project, or, otherwise, running to the extremity of the protuberances 

 and antenna-like processes, Avhich are also armed with bristles. Daliymple 

 noticed nerves so disinbaiedm Notommata anylica ; and Leydig has indicated 

 the like in many species. The supply of a nerve to the so-called siphon or 

 respiratory tube imparts to it the character of an antenna, tactile organ, or 

 feeler. The evident delicate band or cord seen within the tubular process of 

 Melicerta is indeed called by Mr. Williamson a muscular band ; yet at least 

 some portion of it must be esteemed a nerve-cord, if the organ in question 

 really possesses tactile powers. 



A similar distribution of nerves is witnessed in the Turbellaria, and, as 

 Leydig says, among the Phyllopoda and Arthropoda. 



Nei-vous substance has its origin in simple cells, which in ganglia retain 

 their cellular character, but in nen^es appear to be elongated as tubes, — the 

 ceU-wall constituting the nerve-sheath or the neurilemma — the cell- contents 

 (the contained nerve-tissue) existing as a fine molecular matter. In nerve- 

 masses or ganghons the original nuclei remain, and the several constituent 

 cells are aggregated and held together by diffused connective tissue. Some 

 pecuHar structures, supposed to stand in especial relation to the nervous 

 system, are described by Leydig. We cannot do better than follow his 

 account in an abstract. 



Immediately above or about the brain-ganglion, in many genera, a sac is 

 observable fiUed with a whitish substance, called by Ehrenberg the " chalk- 

 sac " (Kalkbeutel). Leydig confesses that he has hitherto been unable to 

 determine whether this sac is in immediate connexion with the brain, or in- 

 dependent of it. In Notommata centrura (XXXYIII. 26 t) it appears as a 

 process or lobe of the brain; but in another species, N. aurita, the sac is so 

 elongated as to form a thin stem filled with the chalk-like matter, which it 

 seems to discharge by an opening on the head. This organ would therefore 

 seem to partake of the nature of a gland. Beside the genera named, this sac 

 is seen in Notommata trijpus, in N collans, and in iV' tardiyrada ; also, if the 

 black speck noticed by Perty be the same structure, in N. roseola. Ehrenberg 

 refers to its existence in Diylena, Meyalotrocha, and Brachionus ; but in the 

 last-named genus Leydig has failed to discover it. 



The vesicular space or sac is, in several instances, not single ; but two, 

 three, or four are noticeable. Thus in Meyalotrocha Ehrenberg mentions four 

 opaque, white, spherical bodies at the base of the rotary organ. 



Another sac, distinct from the foregoing, is seen in EiicJdanis and Notom- 

 mata centrura, lying in the median line close above the brain, and discharging 

 itself by a duct passing forwards to the cuticle. It contains no chalky matter, 

 but is translucent and composed of clear cells. The peculiar and considerable 

 organ which Leydig met with in Stephanoceros, placed in advance of the sto- 

 mach, and consisting of a group of hyaline vesicles with a discharging orifice 



