420 
EDWIN S. GOODRICH. 
cirrus must be classified with Protodrilus, and Saccocirrus has 
parapodia with chaetse on most of the segments of the trunk. 
This conclusion has been remarkably confirmed by the happy 
discovery made by Moore (17), of a genus allied to Polygordius, 
Chsetogordius, bearing chaetae on some segments. Salensky 
and Pierantoui (19, 14) also agree that Protodrilus is closely 
allied to Saccocirrus. Taken as a whole the Archiannelida 
form a degenerating series which can only be read one wav. 
But very possibly the group includes three such series start- 
ing from a common Chastopod ancestor, Chaetogordius and 
Polygordius forming one, Saccocirrus and Protodrilus 
another, and Nerilla, Dinophilus, and Histriobdella a third. 
Summary. 
Nerilla is an Archiannelid, with a prostornium, a pygidium, 
and nine trunk segments bearing parapodia. There are three 
cirri on the prostornium, two on the pygidium, and one on 
each parapodium except the last. The cirri are slender, 
hollow, jointed processes, with sensory hairs. A ventral 
ciliated groove extends from mouth to anus ; ciliated rings 
occur on the prostornium and on the trunk segments, and 
there is a ciliated patch on each side of each segment. The 
first parapodium bears one bundle, and the other parapodia 
two bundles of simple chaetae. The cirrus is placed between 
the bundles. The central nervous system, throughout closely 
connected with the epidermis, consists of a brain and two 
ventral nerve-cords without ganglionic swellings. The 
prostornium carries four eyes and two nuchal organs. The 
alimentary canal consists of an oesophagus, stomach, intestine 
and short rectum, all ciliated, and a ventral muscular 
pharynx. Unicellular glands open into the buccal cavity, and 
gland-cells are greatly developed on either side of the stomach. 
The coelom is well developed; but some of the septa are very 
incomplete. Coelomic corpuscles are very rare; a delicate 
network of coelenchyme extends throughout the body-cavity. 
A simple vascular system is present. The nephridia have 
