No. I.] SENSE-ORGANS OF LUMBRICUS AGRICOLA. 22 1 



description and illustration of the sense-organs of Lumbricus 

 than any of his predecessors, added little to our knowledge of 

 their structure. He likened the mode of arrangement of the 

 cells in a sense-organ to the overlapping scales in an onion. 

 A section through the outer surface of a sense-organ, conse- 

 quently through the covering cells, does often give this appear- 

 ance, but a good section through the center of an organ shows 

 that there is no regularity in the arrangement of its cells. 

 Cerfontaine gave the first satisfactory figure of the cuticular 

 markings. Lenhossek ('92) and Retzius ('92, a and b) both 

 denied the existence of definite sense-organs. The titles of 

 some of the papers which contain descriptions of these organs 

 appear in the footnotes to Lenhossek's article, but these de- 

 scriptions are not referred to in his paper. It seems to me 

 that no observer has correctly described the cells of the sense- 

 organs.^ 



^ An article entitled " Zur vergleichenden Anatomie der Oligochaeten " by Dr. 

 Richard Hesse has recently appeared in the Zeit. f. wissen. Zoologie, — Bd. 58, 

 p. 394, 1894, — in which the writer correctly describes the sense-cells and also 

 arrives at the same conclusion concerning the nerve-cells of Lenhossek as I have 

 presented. Hesse worked on several species of Lumbricidae, one of which, Lum- 

 bricus herculeus, Sav., is the same as that upon which I worked. Our results 

 on this species are in general confirmatory ; they differ in the following points : 

 (i) Hesse finds in a sense-organ supporting as well as sense-cells, but does not 

 note the small basal cells. He describes these supporting cells as of the same 

 width throughout. I have looked through my preparations again, tracing single 

 sense-organs through all their sections, and I feel warranted in believing that such 

 supporting cells do not regularly form a part of a sense-organ. I have found, in 

 organ after organ, nothing but cells which tapey- to both ends from the enlarged 

 part in which the nucleus lies, and which end in a hair-like process passing through 

 the cuticula. Moreover, I have found that the number of sense-hairs seen in a 

 given section of a sense-organ corresponds to the number of cells in that section ; 

 and the number of pores over a sense-organ — as shown in the cuticular markings 

 — corresponds to the number of cells usually present in a sense-organ of the same 

 region. Sections which give cross-sections of sense-organs show that these organs 

 often have one side deeply indented. In such cases, a longitudinal section of the 

 same organ on this side would have shown some of the covei-ing c€^?. between the 

 sense-cells, and these covering cells would appear like the supporting cells de- 

 scribed and figured by Hesse. I would therefore consider that, if a sense-organ 

 contains any supporting cells, these do not differ in form or peripheral ending 

 from the sense-cells. (2) Hesse believes that the sense-organs in a given meta- 

 mere "auf drei Giirteln liegen, die um das Segment herumlaufen." Of these his 

 " mittlere Giirtel " must correspond to my median zone, while his " vordere " and 

 " hintere Giirtel " must be composed of some of the small organs irregularly dis- 



