METAZOA VERMES. 305 



ANNELIDA. OLIGOCHAETA. 



Transitional forms between the marine Chaetopoda 

 and the terrestrial Oligochaeta may be represented by 

 Manayunkia speciosa Leidy. This little tube-worm in- 

 habits fresh water, while at the same time, according to 

 its discoverer, it is related to the marine worms, especi- 

 ally to Fabricia, a near ally of Terebella. 



In the development of Manayunkia the free-swimming 

 stage is skipped and even the embryo (PI. 758, figs. 2, 3) 

 that develops from the egg (fig. i) has lost its cilia. The 

 different stages of the larva (figs. 4-6) are passed within 

 the tube, and thus the young are "retained under the 

 care of the parent until sufficiently developed to be able 

 to care for themselves." 1 Both larvae and adult (fig. 70 

 are divided into a small number of segments. The adult 

 is abundantly supplied with tentacles. There are no 

 parapodia, but each segment is provided on either side 

 with a cluster of setae. These organs are small and 

 generally few in number, as compared with the numerous 

 strong bristles of Chaetopods ; hence the name of Oligo- 

 chaeta. 



The terrestrial Oligochaeta are represented by the 

 common earthworm, Lumbricus terrestris Linn. (Nos. 

 759, 760). Although a land animal, it is able, according 

 to Romanes 2 to live in water nearly four months. 



The eggs of the earthworm are laid in cocoons or egg- 

 cases and the free-swimming larval stages are wholly 

 skipped, so that the worm acquires the form of the adult 

 before leaving the egg. 



The peculiar iridescence already observed on marine 

 worms is well seen when the earthworm is immersed in 

 water and placed in the sunshine. 



1 Leidy, Proc. Acad. Nat. Sci. Phila., 1883, p. 209. 

 'Nature, XXIV, 1881, p. 553. 



