XC INTRODUCTION. 



absent altogether ; in some cases it occurs in great abun- 

 dance*. 



As I have already stated, this organ is the channel 

 through which the immense numbers of spermatozoa, con- 

 gregated in certain cases and at certain seasons in some 

 of the zooecia, find their way into the water. I have 

 watched them streaming up incessantly from the lower 

 part of the cavity for three or four minutes, the filaments 

 as they reached the base of the organ being drawn into it 

 and carried through it by the action of the cilia, and then 

 ejected and borne away by the tentacular currents. After 

 a while a single filament made its appearance occasionally ; 

 and at last none were to be seen. This swarming of the 

 spermatozoa is really an extraordinary sight; and the 

 numbers expelled in the course of it must be immense. 



At other times I have repeatedly seen a mass of excre- 

 mentitious matter pass into the organ from below, which 

 was gradually forced upwards by the cilia, and at last 

 ejected, as a pellet, through the terminal orifice. This, I 

 confess, surprised me not a little, as in some cases in 

 which the organ was present the faecal matter was seen 

 to pass outward in the usual way through the anal opening. 

 I was at one time inclined to regard this curious appendage 

 as denoting a difference of sex ; but as I have met with it 



* Ehlers suggests that this intertentacular organ may be nothing more or 

 less than a parasite, as he had himself noticed a very similar structure on a 

 Lepralia, which he had ascertained to be an infusorium ! We may safely 

 conclude that he contented himself with referring to my paper, and dispensed 

 with the reading of it, as it would be difficult to harmonize the very precise 

 description which it contains of the passage of the spermatozoa through the 

 cavity of the organ with any such hypothesis. 



The curious structure which he has himself noticed as occurring on Hypo- 

 phorella (op. cit. p. 56), and which has no doubt an excretory function, may 

 very probably bear some analogy to the organ which he has too hastily dis- 

 missed as apocryphal. 



