NEREIS DIVERSICOLOR. 819 



ordinary type, and the other of this colour in the anterior fourth, whilst the rest is of a 

 grass-green tint. He considers that the latter (green) colour is due to a diet of green 

 Algae, a condition which is not in accordance with the observations at St. Andrews, where 

 the greenish hue appeared to be the result of the presence of masses of more or less ripe 

 ova. There is no reason, however, why a diet of JJlva or other green Alga should not 

 tint the digestive canal green. 



In the male the sperm-cells fill the various cavities even to the bases of the dorsal 

 cirri throughout January, but though the body- wall is frequently distended, no degenera- 

 tion of the muscular bands can be observed. In the females the size and abundance of 

 the ova in particular examples vary, but, as a rule, the granular ova with a slightly 

 stained nucleus and a more deeply stained nucleolus are more or less advanced towards 

 maturity. Occasionally an example with few and small ova appears. In some of these 

 the muscular walls of the body are contracted, and very few ova, and these of small size, 

 occur in the perivisceral space. More frequently they are found in the feet. Masses of 

 ovigerous tissue are attached to the vessels near the bases of the latter ; and cellular 

 masses (it may be parts of the dorsal organ) with boldly stained nuclei pass upward at 

 the bases of the feet within, as well as without, the lateral lobe of the dorsal longitudinal 

 muscles, and in specimens having a considerable number of large ova similar cells pass 

 into all the spaces of the feet. These loose coelomic masses probably represent the 

 cells alluded to in the living forms. 



In February the increase in size and the division of the sperm-cells form the most 

 noteworthy feature, but no free sperms are seen. In the other sex the ova in many have 

 considerably increased in size, and from the appearance of the annelids a large number of 

 ova must have been discharged. 



Signs of rapid division of the sperm-cells characterize many males in the middle of 

 March, and towards the end of the month the perivisceral cavity forms a vast reservoir 

 for the male elements. The body-walls are stretched, the muscular layers diminished, and 

 the alimentary canal collapsed. The tubes of the segmental organ have also enlarged, so 

 that sperms could readily find issue by the segmental papilla. Though the nuclei of the 

 walls of the organ and its tubes are everywhere distinct, no trace of sperms was at any 

 time found within it, so that they probably escape by rupture of the body-wall, as in 

 allied forms. 



The ova in the various examples throughout March appear to attain fall size and 

 maturity, and they are remarkably large, viz., about '1524 mm., and they are probably 

 shed by rupture of the bod}- wall, the vast numbers set free, even from a limited area, 

 affording an indication of the almost illimitable resources of nature in the sea. Whether 

 the sexes discharge their elements in situ or by a terminal pelagic stage could not be 

 ascertained. None were captured in the tow-nets dragged, by day and by night, up 

 stream at ebb-tide, and no indication of any change in the structure of the feet, bristles, 

 or eyes, and no shrivelling of the posterior region of the body as in the very interesting 

 Ceratocephalus Osawai of Akira Izuka, 1 common in the estuary of the Sumicla River in 

 Tokyo, occurred. If one may hazard a conjecture, it is probable that the sperms and ova 

 are discharged on the sites inhabited by the annelids, and the larvae by-and-by carried 

 1 ' Journ. Coll. Sc. Univ. Tokyo/ vol. xvii, art. ii (1902). 



