508 POLYZOA 



M. Prouho further throws light on a much contested subject ; 

 namely, the nature of the so-called " intertentacular organ " 

 (i, Fig. 234, p. 469), described so long ago as 1837 by Farre, 1 

 but looked for in vain by the majority of later observers. 



The failure to find this organ, even in species which possess 

 it, in certain individuals, according to Farre's statements, is now 

 satisfactorily explained by M. Prouho, who shows that while it 

 is absent in a large number of polypides, it is normally present 

 in those individuals which possess an ovary, and in those only ; 

 and that its primary function is that of an oviduct. 



The intertentacular organ is an unpaired ciliated tube, which 

 is situated between the two tentacles which are nearest to the 

 ganglion. In the retracted condition of the polypide, it opens 

 from the body-cavity into the tentacle-sheath ; and in the 

 expanded condition, directly to the exterior. 



In the remarkable case of Aleyonidium duplex, each zooecium 

 normally possesses two sexual polypides. The first of these 

 produces a testis and then becomes a " brown body." The 

 second is meanwhile developed, and produces an ovary and an 

 intertentacular organ, a structure which was not present in the 

 male polypide. The eggs pass through the intertentacular organ 

 into the tentacle-sheath, and attach themselves to the diaphragm 

 {d, Fig. 234), where they remain during their development. 



Although the intertentacular organ has been found by Prouho 

 in female polypides only, it would perhaps be going too far to 

 assert that it is confined to polypides of that sex. Hincks 2 

 has observed the passage of spermatozoa in enormous numbers 

 through the organ, although it may be noted that there is no 

 sufficient proof that eggs were not present as well in these 

 zooecia. It further appears that in some cases waste matters 

 may be removed from the body-cavity through the same passage. 



It may be presumed that the egg is normally fertilised by a 

 spermatozoon, although this is at present largely a matter of 

 inference. It is believed by Joliet 3 that fertilisation is reciprocal, 

 although Prouho has come to the opposite conclusion. Joliet 

 has, however, very justly pointed out that the enormous number 

 of spermatozoa developed by a single individual would be dispro- 

 portionately large, if their function were merely to fertilise the 



1 Phil. Trans. 1837, p. 408. 2 Brit. Marine Polyzoa, Introduction, pp. lxxxvi, xc. 

 3 Arch. Zool. Exp. vi. 1877, p. 261. 



