Miscellaneous. 147 



The median and inferior regions alone present segmental organs in 

 pairs in each segment ; the superior region never possesses any. 

 Contrary to opinion, these organs are not contained in a single 

 segment : they alwaj's commence in one segment and terminate in 

 the following one ; so that the first segment of the median region 

 only contains portions of two segmental organs. Each segmental 

 organ is formed by an internal orifice surrounded by a half-vestibule, 

 and an excretory tube, which is continued into a spacious sac, and 

 this opens externally through a short duct. 



Each segment is separated from the following one by a diaphragm. 

 Near the line formed by the union of this diaphragm with the 

 integument is situated, on each side, the vestibule of the segmental 

 organ. Its form resembles that of the sigmoid valves of the heart, 

 and its inner surface is uniformly lined with vibratile cilia. The 

 excretory tube follows the vestibule, and is entirely contained in 

 the following segment ; it is easily distinguished, even in the living 

 animal, by its brownish colour. It is attached to the postero- 

 internal surface of the large ventral muscle of the same side, and 

 travels in a more or less curved direction in the different segments. 

 At the level of the pedal ramus it widens considerably to form 

 the dilated sac which follows it. This sac almost completely fills 

 the cavity situated in the base of the dorsal ramus and opens exter- 

 nally by a short duct, having its external orifice upon the lower 

 surface of the ramus. The inner walls of the whole segmental organ 

 possess an epithelium with highly developed vibratile cilia, causing 

 a current from within outwards. 



The tissue of the walls of the segmental organ is composed of 

 elements resembling those of the organ of Eojanus in the MoUusca. 

 When separated these cells present a spherical form ; thej^ contain 

 a large nucleus presenting one or more concretions, which may 

 increase in volume, unite and form a calculus, almost entirely filling 

 the cell. These calculi are often found free in the cavity of the 

 organ, and it is to these concretions that its general brownish colour 

 is due. 



The sexes are separate ; the testes and ovaries are nearly of the 

 same form and position. They are mesenteroid cushions placed in 

 pairs in each of the segments and attached to the upper surface of 

 the partitions. Each testis or ovary has the form of a crescent, 

 with the concavity turned towards the digestive tube. In both 

 cases the cushion presents a great number of convolutions, united 

 with the diaphragm by a very small mesentery, and never presenting 

 an internal cavity. The products of reproduction are develoj^ed at 

 the periphery and fall into the general cavity of the body, which, 

 at the time of reproduction, is entirely filled with ova or spermato- 

 zoids. These products give a distinctive colouring to the two sexes 

 — the males are dead- white, and the females have a slight rosy tint, 

 — Comptes Renchis, July 11, 1887, p. 125. 



