4 Mr. C. Darwin on the Structure and Propagation of Sagitta. 



system in a lesser stage of development, the tail contained very 

 little granular matter ; and in proportion as this was less in quan- 

 tity, so was the circulation less and less vigorous : in some spe- 

 cimens no granular matter, and perhaps, consequently, no circu- 

 lation, was visible. 



When the tail is filled with vigorously circulating matter two 

 large cul-de-sacs or gut-shaped ovaries are invariably present, ex- 

 tending, as represented [o o) in the diagram, from the base of the 

 tail along each side of the intestinal tube. These are filled with ova, 

 which in the same animal are in diiferent stages of development, 

 and vary in length from y^o*^ ^^ Jo^^ ^^ ^^ ^^^^ > ^^^^^ shape is 

 pointed oval (Plate I. fig. B), and they are attached by the pointed 

 end in rows to the sides of the ovaries : those of full size are de- 

 tached by a very slight touch. When the ovaries contain many 

 eggs nearly perfect (but not at other times), a small conical and 

 apparently perforated protuberance can be seen on each side (A A) 

 of the body, through which without doubt the eggs are expelled. 

 In dififerent individuals the ovaries are of difi'erent sizes and the 

 eggs in different stages of development : before any of the eggs 

 are perfected the ovaries are merely filled with granular matter ; 

 but this is invariably of a coarser texture than that within the 

 tail. The ovaries when not containing granular matter are con- 

 tracted into a very small size* (B). In great numbers of speci- 

 mens taken in latitude 18° S. and between 37^ and 40° S., I in- 

 variably observed that there existed a close relationship between 

 the quantity of circulating matter within the tail and the size of 

 the ovaries ; from this circumstance, and from the similarity of 

 the granular matter in the ovaries, before any of the eggs are per- 

 fected, with that in the tail, except that the granules are in this 

 latter part of less size, I think it almost certain that the granular 

 matter is first formed within the tail, and that it then passes into 

 the ovaries, where it is gradually developed into ova. I could not, 

 however, trace any opening from the one part into the other, but 

 at the bottom of each ovary there was a space, where a closed 

 orifice might have been situated. 



A well- developed egg presents, when liberated by a touch from 

 a torn open ovary, the appearance represented at (B) in the 

 diagram. The egg is transparent, and contains within it an ex- 

 ceedingly minute globule. Twice on one day and once again a 

 week afterwards, I clearly observed the following curious phseno- 

 menon take place : the apex of the egg, a few minutes after ha- 

 ving been liberated from its attachment, began and continued to 



* I also remark in my MS. notes, that the granular matter within the 

 tail is sometimes contracted into small kidney-shaped bodies ; I cannot help 

 suspecting that I ought in every case to have written that the ovaries were 

 contracted into this form. 



