284 APPENDIX. 



With the obtuse anterior end, which is in constant motion and 

 change, it feels the way, and pushing aside the floating particles that 

 annoy it, it guides itself with as much safety, and appears as careful 

 of obstacles, as if indeed eyes and feelers were sentinels in front. 



II. TERETULARIA (page 18). 



Char. Worms individual, free, very rarely tubicolous, with or 

 without eyes : body soft, cavernous, linear, flat or somewhat cylin- 

 drical, much longer than broad, (very often) clothed with vibratile 

 cilia, sometimes extraordinarily contractile and then generally sepa- 

 rating into several pieces by a transverse division. Sucker none. 

 Head continuous with the body or indistinctly defined, entire or 

 furnished with lobes, raised plaits or fissures (perhaps connected 

 with respiration). Mouth anterior and subterminal, in the form 

 of a slit, for the most part provided with a protrusile long proboscis. 

 (Esophagus short : csecal pouches in a series on each side of the 

 body. Intestine simple (without an anus). System of circulation 

 closed ; two hearts. Nervous system distinct. Sexes separate, but 

 alike in external appearance ; and the cavity containing the testicles 

 and ovaries are alike, excepting in the contents being in the one 

 spermatozoa, and in the other ovules. Female aperture (often mis- 

 taken for the mouth) situated sometimes below the head, sometimes 

 large and sucker-like, sometimes posterior and nearly terminal, when 

 it has been mistaken for an anus. Multiply by ovules, and perhaps 

 by transverse sections. Progress by gliding, and some exude a copious 

 mucus. — All are marine*. 



These worms are of a linear form and very contractile, so that 

 when extended in the act of moving through the water or mud, they 

 exceed their length when at rest by three, four or more measures. 

 They are soft and glutinous, but with more firmness of structure 

 than their appearance indicates ; and to the naked eye they are per- 

 fectly smooth, exhibiting no trace of articulations or wrinkles, though 

 when contracted and viewed through a magnifier, we find that the 

 margins are minutely crenulate. The anterior extremity is usually 

 marked by several black specks arranged on each side of it, variable 



* The following is De Quatrefages' classification of this tribe : — 



A. Nervous trunks entirely lateral. 



"^ Mouth subterminal, inferior Valencinia. 



** Mouth terminal. 



Body very long and flat Borlasia. 



Body very long, more or less rounded Nemertes. 



Body short, proteiform Polia. 



Body short, not variable in form Cerebratulus. 



B. Nervous trunks sublateral Oerstedia. 



