380 PROF. AV. J. DAKIN ON THE 



for its constant piesence and the ducts opening into it. Following 

 the vesicle the nephridium is divisible into two marked sections, 

 a tubular portion and a terminal chamber. The tube describes a 

 I'ough circle and then turns abruptly on itself, so that its termin- 

 ation is close to the vesicle referred to above (see PI. IV. fig. 11). 



The terminal chamber (PI. lY. fig. 1 1, Coe.) is now well known, 

 although missed by the first investigators, who believed that the 

 nephridia opened into the lateral compartment of tlie body. 

 The chamber lies partly above and partly po.sterior to the col- 

 lecting vesicle referred to above. 



The first portion of the nephridinl tube internal to the 

 collecting vesicle is lined by a very delicate and characteristic 

 epithelium of large flat cells. As a consequence of the size of 

 the cells relative to the diameter of the duct it is possible to have 

 transverse sections with only two or thi-ee nuclei showing (see 

 PI. TV. fi^g. 11). The greater part of the nephridium between the 

 terminal chamber and the collecting vesicle is built in this way. 

 The section, however, which actually opens into the terminal 

 chamber is very different. Tlie wall of the nephridium becomes 

 thicker nnd far less delicate and is formed of a compact layer of 

 columnar epithelial cells (see PI. TV. fig. 11, Cil.R.). These 

 cells ai-e so crowded and the nuclei stain so distinctly that most 

 previous workers have noted the peculiarity. In fact this change 

 in the characrer of the cells has been taken as indicating the 

 passage from the ectodermal part of the nephiidium to the 

 mesodermal portion (see Glen, Q. J. M. S. 1918, vol. Ixiii.). 



Now it is the cells of this section of the nephridium which bear 

 the cilia (Pis. III.-IV. figs. 11 & 12). These are so long tha,t 

 after projecting from the cell they extend along the lumen of the 

 duct for a relatively considerable distance. It is extraordinary 

 that in many figur-es showing the structure of the nephridia of 

 Peripatus details of the histology are given at a high magn ill cation, 

 yet no indication of cilia is presented. 



Bundles of long cilia are very characteristic of renal cells, 

 although at the same time they are in the highest degree peculiar 

 for the arthropoda. The Annelid i-esemblances of Perijjatus 

 are certainly heightened as a result of the examination of well- 

 preserved sections through the ciliated ducts of these nephridia*. 



* Since writing- the above I have been enabled to examine a copy of Gaff'rou's 

 famous paper (8) on the Anatomy and Histology of Peripatus, in which the first 

 mention of the presence of cilia in this animal — in the Receptacnla seminis — was 

 made. Looking through his description of the nephridia I found to my surprise 

 the following lines referring to the region where the duct opens into the coelomic 

 vesich^ It must be remembered that the vesicle was unknown at the tin.e, and its 

 remains were supposed to be a funnel-like nephrostome opening into the body-cavity. 

 " Er besitzt wis der Tricliter selbst, kleinzelliges, im Leben ivahrscheinUeh wim- 

 perndes Epithel . . . ." Gatfron never indicates that he found cilia here nor are 

 any shown in his illustrations of this region. We must conclude that the remark 

 was mer(;ly a conjecture, probably suggested by the apparent resemblance to the 

 open nephrostome of an annelid. It is curious, however, that his successors who 

 have studied the nepiiiidia have not commented on this. Either Utv. cilia are only 

 found in the West Australian Veripatoides or else my preparations must be par- 

 ticularly favourable ones. 



