Glass 1. Chcetopoda. Order 1. Polychceta. 173' 



be present. Sexes separate (with some exceptions). A metamorphosis. 

 Marine. 



The following forms are given as examples of this very numerous 

 group. 



1. The Nereidae (Nereis) ha.\e a vei-y elongate body. The prostomium is 

 fTirnislied with foui- small eyes. Noto- and neuro-podia fused ; gills absent. The 

 protrusible pharynx has a pair of hard ohitinous jaws. One species of this 

 genus (N. diversicolor) is oonunon on English coasts, creeping, or swimming, or 

 boring into the sand. 



2. The Polynoidse exhibit a form which, in comparison with that of other 

 Chsetopods, is usually very short and broad, and is especially distinguished by 

 having on the dorsal side a varying number of large scale-like epidei-mal plates ; 

 these plates are modified dorsal cin-i, and are only present on a few segments, 

 the others being provided with cu-ri of the ordinary form. Gills are want- 

 ing. Polynoe squamata with rough, uneven dorsal plates ; the Sea-mouse 

 (Aphrodite aculeata), has the dorsal scales covered with the very long felt-like 

 choetaB of the notopodia, forming a felted mat over the back of the animal ; other 

 dorsal chsetse are thin hairs with a metallic lustre, and others again are stiff, 

 thick opaque spines. Both on English coasts. 



3. The Lug worm (Arenicola piscatorum) . Fi'ont part of cylindiical body 

 swollen, skin rough. Prostomium and peristomium without appendages ; eyes 

 wanting. Noto- and neuro-podia separate, short; the latter a low transverse 

 ridge with a few hooked chsetse standing from it; both without ciiTi. Gills 

 present only in the middle region of the body, but here weU-developed. Para- 

 podia wanting on the hindmost third of the body. The proboscis without teeth. 

 The Lugworm lives in the sand, burrowing close to the shore ; it swallows the 

 sand for the sake of the contained organic particles, the excreta are deposited on 

 the shore, above the holes, as castings. Yery frequent on these coasts (used as 

 bait for fish). 



4. The Serpulidse (Serpula) live in fixed calcareous tubes, which are either 

 in-egularly or spirally coiled. When undistm'bed, the anima! projects fi-om 

 the tube a large number of long threads provided with a double row of delicate 

 lateral branches, which are an-anged in two gi-oups on the prostomium. These 

 feather -like thi-eads are respiratory, and by means of their oiha di-ive micro- 

 scopic organisms into the mouth. One of the thi-eads is specially strong, 

 without lateral branches, and with a calcareous operculum of varying foi-m at 

 the end. When the animal is irritated it withdraws the whole bunch of threads 

 into the tube, which it closes with the operculum. At the anterior end of 

 the animal the notopodia are provided with hair-like chsetse, the neuropodia 

 with hooked chsetse, whilst the converse is the case on the gi-eater part of the 

 posterior extremity. Several species on sea- weeds, stones, etc., on English coasts. 



Order 2. Oligochseta. 



The prostomium and perLstomium are almost always without ap- 

 pendages. The parapodia are represented only by bundles of cheetae 

 (quite a few in each bundle), no cirri ; gills wanting. Hermaphrodite. 

 No metamorphosis. 



The Oligochseta live with few exceptions in fresh water or in the 

 earth. Compared with the Polychseta there are few species. 



1. Earthworms (Lumhricus) have elongate cylindrical bodies pointed 

 anteriorly. Each segment is provided with foiu' bimdles of chBetse, with only two 



