EMBRYONIC DEVELOPMENT OF ANNELIDS. 629 



gressively increases by the interposition of new ones between the 

 caudal and its preceding segments ; the various internal organs 

 become more and more distinct, Eye-spots make their appearance, 

 little bristly appendages are put-forth from the segments, and the 

 animal gradually assumes the likeness of its parent ; a few days 

 being passed by the Tubicolar kinds, however, in the actively- 

 moving condition, before they settle down to the formation of a 

 Tube.* 



490. To carry-out any systematic observations on the Embryonic 

 Development of Annelids, the Eggs should be searched-for in the 

 situations which these animals haunt ; but in places where Anne- 

 lids abound, free-swimming Larvae are often to be obtained at the 

 same time and in the same manner as small Medusae (§ 421) ; and 

 there is probably no part of our coasts off which some very curious 

 forms may not be met with. — The following may be specially men- 

 tioned as departing widely from the ordinary type, and as in them- 

 selves extremely beautiful objects. — The Actinotrocha (Fig. 328) 

 bears a strong resemblance in many particulars to the Bipinnarian 

 Larva of a Star-fish (§ 441), having an elongated body, with a series 

 of Ciliated Tentacula (d) symmetrically arranged ; these Tentacula, 

 however, proceed from a sort of Disk which somewhat resembles 

 the 'Lophophore' of certain Polyzoa (§ 446). The Mouth (e) is 

 concealed by a broad but pointed hood or 'epistome' (a), which 

 sometimes closes-down upon the tentacular disk, but is sometimes 

 raised and extended forwards. The nearly cylindrical body termi- 

 nates abruptly at the other extremity, where the Anal orifice of 

 the Intestine (b) is surrounded by a circlet of very large Cilia. 

 This animal swims with great activity, sometimes by the Tenta- 

 cular Cilia, sometimes by the Anal circlet, sometimes by both 

 combined ; and besides its movement of progression, it frequently 

 doubles itself together, so as to bring the Anal extremity and the 

 Epistome almost into contact. It is so transparent that the whole 

 of its alimentary canal may be as distinctly seen as that of Bower- 

 bankia (§ 449) ; and, as in that Polyzoon, the alimentary masses 

 often to be seen in the Stomach (c) are kept in a continual whirl- 

 ing movement by the agency of Cilia with which its walls are 

 clothed. This very interesting creature was for a long time a 



the ordinary form of a Marine Worm three or four times its previous 

 length, and the Ciliated Disk entirely disappeared. An accident unfor- 

 tunately prevented the more minute examination of this Worm, which 

 the Author would have otherwise made ; but he may state that he is 

 certain that there was no fallacy as to the fact above stated ; this Larva 

 having been placed by itself in a cell, on purpose that it might be care- 

 fully studied, and having been only laid aside for a short time whilst 

 other selections were being made from the same gathering of the Tow- 

 net. 



* See especially the admirable Memoir of Prof. Milne-Edwards ' Sur le 

 Developpement dcs Annelides,' in the " Ann. des Sci. Nat.," Ser. 3, Zooh, 

 Tom. iii. ; and the recent Systematic Treatise of M. de Quatrefages, 

 entitled, " Histoire Naturelle des Annelides," in the " Suites a Buff on." 



