113 



The Naviculae and Frustuliae place themselves, two 

 and two on the side of their pedal surface, and re- 

 main sometimes whole days in that position , and 

 separate themselves again. I have seen a pair of 

 the Frustulia ayrestis (fig. 14. a.) united in this 

 way, go slowly asunder, and remarked that, in spite 

 of that apparent separation , both individuals were 

 joined by two very narrow tubes (fig. 14. b. c. ). 

 And in magnifying them still more , I observed that 

 these tubes passed through the cuirass and com- 

 municated with the brown content. I saw also upon 

 the orifice of the tubes an areola forming itself by 

 a thicker and darker content. They remained united 

 about an hour, after which the separation took place 

 as follows: The tube (c.) drew back in the animal- 

 cule (fig. 14. b.), and the tube (d.) towards (f.). 

 Soon afterwards, having been able to observe the 

 animalcule (f.) from downwards , or from the pedal 

 surface, I saw (fig. 15.) in the middle line upon (d.) 

 a larger opening , and upon (c.) a smaller one. In 

 the last, the tube (fig. 14. b. d.) had drawn back; 

 and the tube of the other animalcule entered into the 

 first. In looking sidewise, I discovered, though rather 

 indistinctly, both openings (d. c.). 



Under the opening of the mouth, we find in the 

 Pharyngoglossa, under the middle line and under the 

 alimentary tube, a small round wart (fig. 16. d. and 

 16. b. d.), perforated in the middle, of a very doubtful 

 function, and which, considering its position, I bring 

 under this head. 



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