•no Dr. O. vom Rath on the 



As regards tlic sense-organs of tlic Pliyllopods, e. g. Brancln- 

 pits, the views of authors are divided. According to Leydig 

 (loc. ci't.) and Spangenberg *, two ganglion-cells, lying one 

 behind the other, belong to each sensory hair; Clans t was 

 able to distinguish only one ganglion-cell ; in connexion with 

 the sensory hairs of Branchijnis I always counted from three 

 to four cells, and from four to five beneath those of Apus. 

 With the sensory hairs of both these Pliyllopods I shall sub- 

 sequently deal at greater length. Among the Cladocera the 

 number of sense-cells belonging to each sensory hair is also 

 tolerably small. 



As regards the histological structure of the nerve-end appa- 

 ratus of the auditory organs, this in no way differs from the 

 description which I have given above. I am unable to eon- 

 firm the statements of authors {e. g. TIensen, loc. cit.), who 

 ascribe only a single ganglion-cell to each auditory hair ; on 

 the contrary, I always found beneath the base of each auditory 

 hair of Astacvs, Siriella, and Mt/si's a distinct group of sense- 

 cells, with terminal cords reaching to the tip of the hair. 



I would here just mention in passing that behind the 

 groups cf sense-cells in the Crustacea I have never found those 

 peculiar large cells of glandular appearance, such as I have 

 described as companion cells (" Begleitzellen ") in the case of 

 the sense-organs of ]\lyriapods and many Insects ; nevertlieless 

 in the neighbourhood of the Crustacean dermal sense-organs 

 there occur, with a certain degree of regularity, on both pairs 

 of antenna?, as well as on the whole of the limbs, irregular 

 groups of tyi)ical gland-cells, which are particularly noticeable 

 in the Amphipoda and Isopoda. 



instance perfectly accurate." The latter remark is liable to be misunder- 

 stood. I therefore lay stress upon the fact that Kiiuckel is certainly in 

 error in holding that in Insects invariably only a single ganglion-cell 

 belongs to all sensory hairs. There are isolated cases, it is true, in which 

 only a single sense-cell is found in connexion with each sensory hair, and 

 I may refer the reader to my statements (Zeitschr. f. wiss. Zool. 40 IM. 

 y, pp. 410 -419) and figures (tigs. 3 h, 10, 10, 32). At that time I had not 

 included the scnse-orgaus of the halteres -within the scope of my investi- 

 gations ; since then I have convinced myself by means of series of sections 

 that it is actually true that only a single large bipolar ganglion-cell 

 belongs to each sense-organ. 



* Spangenberg, " Zur Kenntuis von Branchijms stagnalis,'^ Zeitschr. f. 

 wiss. Zool. 25 Bd. Suppl., 1875. 



t Clans, " Untersuchungen iiber die Organisation uud Entwiclduug yon 

 Branchiims uud Artetnia," Arbeiten aus d. Zool. Institute d. Univ. Wien, 

 1885. 



