No. 2.] AJVATOAfV OF BDELLODRILUS ILLUMINATUS. 529 



one pair (the two limbs of a loop, Fig. 36, ;/), the protoplasm 

 is more uniformly distributed, and the granules show a decided 

 tendency to become arranged in lines radiating from the lumen, 

 as seen also in living cells ; while the protoplasm of the remain- 

 ing pair {forming another loop) is more or less reticulated and 

 less deeply stained (Fig. 16). 



The system of simple tubules is partly concealed in the dark 

 cellular mass mentioned above, where it becomes connected 

 with a series of intra-cellular plexuses — not mere lateral 

 branches of the main lumen, as Bourne has described in cer- 

 tain leeches, but a regular series of actual interruptions of the 

 simple lumen. 1 The course of the tubules within this mass is 

 very irregular and tortuous. Turning abruptly on itself at 

 frequent and regular intervals, the tubule expands into irregu- 

 larly rounded nodules of about three times the ordinary 

 diameter. Within the highly granular protoplasm of these 

 swellings the lumen breaks up into a complex system of ir- 

 regularly branching and communicating canals, all of which 

 converge at the opposite point of the nodule to empty into the 

 next section of the simple tubule (Fig. 39), so that in this 

 region there is a regular alternation of short lengths of simple 

 ciliated canals and irregular plexuses of non-ciliate anastomising 

 canals. The latter may be aptly compared to the communicat- 

 ing passages which termites excavate in the trunks of trees ; 

 but the capacity of the passages relatively to the amount of 

 solid substance between and around them is less in the struc- 

 ture here described. 



Nuclei are present both in the simple segments of the 

 tubules and in the plexus cells (Figs. 38 and 39). Cilia are 

 distributed throughout a considerable portion of the simple 

 tubules, and in the simple canals connecting successive plexuses 

 (Fig. 39) ; and are absent from plexus passages and in the ter- 

 minal segment of the tubule (Fig. 35). No nephrostomes have 

 yet been detected in this species ; but Fig. 40 represents one of 

 B. philadelphicus, which has nephridia of similar structure. 



1 See also Eisen's paper on the remarkable nephro-plexuses of Deltania and 

 Argilophilus which I have read since writing the above. Me?n. Cal. Acad. Sci. 

 Vol. II., No. 3. 1894. 



