12 bulletin: museum of comparative zoology. 



in E. viridis about twelve of the preanal segments are colorless and trans- 

 lucent, not containing any sexual elements. These empty segments are 

 usually much wider than those preceding them, thus marking off a dis- 

 tinct broader preanal region (Fig. 5). The longest specimen measured 

 3 cm, from the material collected by Kramer at Apia. Usually there is 

 present, in each segment, a pair of brownish or blackish pigmented spots 

 at the dorsal base of the parapodia (Fig. 6). These are not comparable 

 to the ventral eye-spots of E. viridis, but rather to the paired pigmented 

 "glands" so common in the Alciopina and Tomopteridae and, possibly, 

 have a photogenic function. Tread well (1900) has described similar 

 paired organs in E. armata. The composition of the parapodia (Fig. 15) 

 is much simpler than in E. viridis. There are two of the simple chsetae, 

 one much longer than the other, and but one of the compound kind. 

 The figure does not show the cirri which are much shorter than in E. 

 viridis, and gill filaments could not be determined ; the figure is inverted. 

 The first detailed account of sexual dimorphism in annelids is by Alex- 

 ander Agassiz (1862) for Autolytus, and Malaquin (1893), has called 

 attention to its occurrence in other Syllidae. In the Nereidae, sexual 

 dimorphism was first described by Ehlers (1868) where it is known for up- 

 wards of twenty species, and it is manifested in different ways pretty much 

 throughout the Annelida. It occurs in two general ways. First, as in 

 the Nereidae, where certain sexual individuals undergo a metamorphosis 

 adapting them for the dissemination of the sexual products (Heteronereis), 

 and secondly as in the Eunicidae ("Palolo"), where certain regions of 

 the animal, containing the sexual elements, become modified and are set 

 free by a process of autotomy. In the first case the metamorphosed in- 

 dividuals are known as the epitokal (Ehlers, 1868) or epigamous (Clap- 

 arede, 1870) forms, in the latter the sexually modified part which is set 

 free is the epitokal part of the animal, the unmodified part, the parent 

 animal, which may or may not regenerate the liberated portion, is the 

 atokal part. In the latter class it is usually the posterior portion that is 

 set free as in Eunice viridis, E. fucata (Mayer, 1900, 1902) Syllidae, 

 etc., while in Ceratocephale osawai (Izuka, 1903), one of the Nereidae, 

 it is the anterior region that leads a free existence. In most epitokal 

 forms there is a great development of the eyes. In the Nereidae, the 

 active epitokal form is attracted by artificial light, and Izuka (1903), 

 states for Ceratocephale that the fishermen attract them by the light of 

 torches, catching them for bait. I have observed the same attraction to 

 artificial light in several forms of Heteronereis. This development of 

 the eyes in epitokal phases of annelids is significant, and as I have pointed 



