608 THE ANIMAL KINGDOM. 



spicuous in Autolytus prolifer {Syllidae), where the male has been described 

 under the generic names, Polybostrichus^ Diploceraea, and Crithida, and the 

 female as Sacconereis. Polymorphic generations are found in Nereis 

 Dumerilii (Claparede). Certain individuals become sexually mature but 

 are of separate sexes ; others appear to become hermaphrodite (= Nereis 

 massiliensis) ; others again are metamorphosed into a Heteronereis, of 

 which two forms are known, one large and tubicolous, the other small and 

 pelagic. 



The Chaetopoda appear to have considerable powers of reparation 

 after injury, and the formation of a new head with anterior somites, and 

 of new posterior .somites has been observed. Phosphorescence occurs in 

 some terrestrial Oligochaeta and some Polychaeta. The light is sapphirine, 

 violet or green ; it appears either over the surface of the body in general, 

 or in certain limited spots, e.g. on the elytra of Polynoe, and is due in 

 some cases to the secretion of unicellular hypodermic glands x . 



The Oligochaeta are either freshwater or terrestrial. The Polychaeta 

 are marine 2 , but a freshwater Lumbriconereis and a Nereid have been 

 found in Trinidad (von Kennel), and a freshwater tubicolous genus, Mana- 

 yunkia, occurs in N. America (Leidy). The Chaetopoda are free except 

 some Tubicola which fix their tubes to stones, shells, or to living animals, 

 e. g. Serpula and Spirorbis to Crabs ; Branchiomma vigilans to Aphro- 

 dite ; and various others to Starfish (Astropecten), or on Sea Urchins 

 (Cidaris). A few Polychaeta are pelagic (Alciopidae, some Phyllodocidae ; 

 Tomopteris ; Typhloscolex) : others only at the reproductive season (Hetero- 

 nereiS) Syllidae). Certain Tubicola bore into rocks or shells (Heterocirrus 

 Dodecaceria^ Polydora ciliata, Sabella saxicavd}. Most Errantia are 

 carnivorous ; the Tubicola and Oligochaeta are vegetable feeders. The only 

 instances of parasitism are the Eunicid Oligognathus Bonelliae in the 

 coelome of the Gephyrean Bonellia, Alciopina parasitica (? a larval Alciope) 

 in a Pleurobrachia (Ctenophora\ an Amphinomidan in the branchial 

 cavity of Lepas anatifera {Cirripidid} 3 , and the family Myzostomidae 

 (infra^ p. 609). Commensalism also occurs ; e. g. Polynoe Scolopendrina and 

 Harmothoe Marphysae inhabit the tunnels of Marphysa sanguined, 



The fixed Tubicola with calcareous tubes are found from the Silurian 

 upwards. Undoubted remains of Errantia occur in the Solenhofen slates, 

 and probably in the Silurian (Nereites, Crossopodid}. Structures from the 



1 For the rosette organs of Tomopteridae, which consist of an assemblage of yellow coloured 

 sacs with a nerve supply, and are apparently phosphorescent organs, see Greeff, Z. W. Z. xlii. p. 440 ; 

 and on the elytra of Polynoe which are phosphorescent, Jourdan, Z. A. viii. 1885. 



2 The Polychaeta live at all depths in the ocean. ' No definite law as to the presence or 

 absence of genera at particular depths can be enunciated,' but ' the majority of abyssal forms are 

 tube-dwellers ' (Mclntosh). A Terebellid Leaena abyssorum and a Serpulid Placostegus benthalianus 

 were dredged by the Challenger in 3212 fathoms. Cf. Challenger Reports, xii. 1885. 



3 Fritz Miillcr, Facts for Darwin, 1869, p. 44. 



