PHORONIS ARCHITECTA— BROOKS AND COWLES. 95 



the externa] opening of the ventral pouch and the nephridial openings are found on the ventral 

 wall of the trunk just posterior to the insertion of the mesentery as in other species. 



Nephridia. — Wagener (2:i) was the first to observe the •"nephridial bouquets," but Caldwell 

 (3) was the first to publish a careful study of the, nephridia of the Actinotrocha. Goodrich" (6) 

 has recently published a paper on the excretory organs of Amphioxws, and lie adds a note on the 

 nephridium of the Actinotrocha which confirms Caldwell's view. The two latter investigators 

 agree that the nephridium ends blindly without funnels; that there are tubular processes, each 

 one containing a lumen and tipped with an excretory cell, and that these processes radiate out 

 from the blind inner end of the nephridial canal. 



Longfchamps (12) is inclined to accept Caldwell's view of the subject. Roule (20) and Ikeda 

 (9) seem to hold the view that the nephridial canal ends blindly without branching, and that the 

 blind end is tipped with excretory cells, which, however, are not perforate. 



Masterman (15) and Menon (17) have another view. They both think that the nephridial 

 canal terminates internally as two (Menon) or more (Masterman) funnels, and they recognize the 

 existence of long processes without lumens attached to the ends of the funnel. 



We have not been able to make a study of the nephridia of the living Actinotrocha, but we have 

 investigated them by means of sections in Species A. and Species B. For this purpose we have 

 used material fixed in Flemming's fluid and also in corrosive acetic. The sections were stained 

 with iron hematoxylin. Our work has been done with very high powers (Zeiss obj. T V and No. 

 12 Zeiss compensating occulare). 



The nephridia of the two Acti/notrochst have much the same structure, but in Species A. 

 we have been unable to find that the internal end of the nephridial canal branches, while in 

 Species B. the internal end divides into two short branches. 



Figs. 52, 52«, 52J represent three transverse sections through the anterior part of the 

 nephridium of Species B. Fig. .">2 is through the nephridial canal just posterior to its inter- 

 nal end. Darkly staining dots seen in the lumen represent cross sections of long flagella such as 

 Goodrich (G) has described in the " solenocytes " of AmpMoxus. 



Fig. b2<i shows a section through the nephridial canal a few sections anterior to that of fig. 

 52, and at the same time it shows the lower or most posterior branch with a few excretory cells 

 and their processes. 



In tig. 525, which is a section through the tip of the upper or anterior branch of the nephrid- 

 ium, the lumen of the nephridial canal is reduced to a very small (dear space. 



If a section is taken in a longitudinal direction through the nephridial canal and its excretory 

 processes (fig. 52g), it is seen that the distinct walls of the nephridial canal disappear when the 

 " bouquet" of excretory cells is reached, but that the end is blind and that it is merely a thin 

 walled bulb from whose surface radiate the processes of the excretory cells. The structure of 

 these processes is the same in both species that we have examined except that in Species A. they 

 are much shorter, which might account for the different descriptions we find in the literature. 

 We are convinced that in both species the excretory processes contain lumens, that these lumens 

 are continuous with the lumen of the nephridial canal, and that they contain flagella. 



Each of the excretory processes is tipped by a body the distal end of which is drawn out 

 into a sharp-pointed process. The outline of only one cell could be seen in the body. Some- 

 times it contains but one nucleus, which may be oval in shape or bent almost at right angles 

 (tig. 52</), but in the majority of cases there are undoubtedly two nuclei (fig. 52c). Fig. 52( 

 shows a cross section through one of these bodies. If a transverse section of the nephridial 

 processes is taken (tig. 52/), it is seen that each has a definite wall and that inside there is a 

 definite dot which we take to be a cross section through the flagelluni. This Hagellum has its 

 origin from the cell body at the end of the process, and the indications are that the Hagellum 

 extends throughout the length of the process into the lumen of tin 1 nephridial tube. 



"Since writing this paper a description of the nephridia of the Actinotrocha by Goodrich (6a) lias come to our 

 notice. Our account agrees to a large extent with his. 



