498 ADAM SEDGWICK. 



other nephridia are open throughout life into the broken-up 

 space of the foot (or lateral sinus?). 



I admit it is rather difificult to make out his exact meaning, 

 his account being somewhat confused and diffuse. But I 

 think I am right in supposing that he maintains in the paper 

 referred to the above four positions. Well, accepting his idea 

 that the later stages resemble one another in the two species, 

 I have no hesitation in saying that he has erred in each par- 

 ticular. The third somite does divide into two parts. The 

 ventral part does not break up into spaces nor does it become 

 traversed by muscles and connective tissue, but persists through 

 life as a vesicle with an epithelial lining. The lateral ramus 

 has nothing to do with the coelom, but comes from the space 

 marked b. lat. in my sections. The funnel of the nephridium 

 opens always into the lateral part of the somite, of which, 

 indeed, it is a part, and does not become blindly closed. The 

 funnels of the other nephridia do not open into the space 

 of the feet, but into the lateral division of their proper 

 somites exactly as do the salivary glands. 



Kennel further maintains that the funnel only of the adult 

 nephridium is mesodermal. I cannot accept this ; it is an 

 altogether fanciful view. It may be true, but it is a point quite 

 impossible to settle by sections. With regard to it, I have 

 only to say that the ectodermal ingrowth at the opening of the 

 nephridura is so extremely inconspicuous that at the early 

 stage, immediately before and after the establishment of the 

 external opening, no such ectodermal part as Kennel describes 

 is present. 



The dorsal divison of the third somite separates from 

 the ventral in an embryo slightly older than that from which 

 series fig. 23 was taken, viz. one in which the cerebral gooves 

 were slightly more advanced than in fig. 23, but not so much 

 developed as in fig. 33, PI. XXXVI. After its separation, it 

 becomes much reduced in size (fig. 36, d. s. 3), then still smaller 

 (PI. XXXVII, fig. 45, d. 5.), and finally vanishes (fig. 46, d. s.). 



This completes what I have to say about the third somite 

 up till Stage f, by which time the adult condition of the parts 



