NEREIS DIVERSICOLOR. 821 



structure of cameratecl shaft and homogomph articulation of the end of the shaft, and are 

 in two bundles in each foot. 



No younger form has yet been found amongst the mud or the adults, so that it is 

 probable that they settle down at this stage. Moreover, no pelagic larvae appeared in the 

 vessels ; but as the post-larval forms with three bristled segments occurred in the mud of 

 the tubes of the adult, it would appear that all do not wander. Yet pelagic Nereids with 

 six bristled segments occur in the tow-nets of the period, but whether of this or other 

 species is yet uncertain. 



When the post-larval form has four bristled segments the head has two eyes on each 

 side, placed close together and posteriorly, a pair of short frontal tentacles, short palpi 

 which present no distal articulation, a pair of tentacular cirri, and two short anal cirri. 

 Behind the head, which bears the tentacular cirri, is a region with only bristles on each 

 side; a foot with a large bristle-tuft and a minute dorsal cirrus follows, and then a second 

 foot of similar structure. A rudimentary foot comes next, with a bristle-tuft on one side. 

 A rudimentary ventral cirrus occurs on each foot. A pair of minute jaws having two 

 teeth behind the anterior fang is found in the proboscis. Vast swarms of Infusoria (like 

 monads) frequent the moist and odoriferous mud in which the young Nereids live. 



The post-larval form of the 28th May (Fig. 73) has a head with two comparatively 

 large frontal tentacles and two stumpy palpi with very short terminal segments that only 

 occasionally are visible, two pairs of tentacular cirri, the last with a spine in the dorsal, 

 five pairs of distinctly bristled feet, with more evident dorsal and ventral cirri and slightly 

 brownish spines, besides two rudimentary ones behind and a large pygidium with two 

 caudal cirri. The cirrus of the first bristled segment is elongating, but the bristles are 

 shorter than in the succeeding foot. The mouth is a wide aperture, followed by the some- 

 what ovoid proboscis, which is armed with two translucent jaws having three prominent 

 teeth which are proportionately longer than in the adult. The proboscis is narrowed 

 posteriorly and joins a large opaque, yellowish, glandular region, broad and truncated in 

 front and diminishing posteriorly and terminating in the pale rectal part of the gut and 

 its dorsal anus. The opaque glandular region stretches from the space between the 

 second and third feet to the last bristled foot, and shows the groups of oily granules so 

 characteristic of the glands on the walls of the alimentary canal. Two slightly opaque 

 ovoid glandular bodies, the segmental organs, lie behind the first complete foot, just in 

 front of the opaque region of the gut, and active ciliary action is occasionally noticed 

 in them. 



In the post-larval form with six bristled feet the eyes are better defined, and the 

 palpi, frontal tentacles, and tentacular cirri are larger. The dorsal cirrus of the first 

 bristled segment is the longest in the animal, but there is no spine. The spines are 

 darker, the posterior end remains bifid, and three teeth occur behind the anterior 

 fang in each jaw. 



When seven bristled feet are present the caudal cirri are considerably longer, the 

 last foot (seventh) having a few short bristles, a short dorsal cirrus, two short spines, and 

 a minute rudiment of a ventral cirrus. Behind is an indication of the eighth foot as a 

 lateral projection, with a minute papilla representing the dorsal cirrus. Internally is the 

 tip of a minute spine, but no bristles. The ventral of the first pair of tentacular cirri 



98 



