CfEPHYREA. CH.ETIFERA. 



389 



the female of Bonellia have the same relations (fig. 31:5). These 

 rudimentary males are furnished (in many species) with two ventral 

 hooks, in front of which in the anterior region is placed the external 

 opening of the vas cleferens. The vas deferens corresponds to the 

 uterus of the female, and is in like manner provided with an internal 

 opening into the body cavity. In Echiurus there are two pairs of 

 brown tubes, which function as generative ducts and reservoirs. 

 In Thalassema there are, according to Kowalevski, three pairs of 

 such tubes. 



The development shows many points of 

 similarity with that of the Annelida. Be- 

 tween the Achceta and Chcetifera, however, 

 there are considerable differences. In both 

 cases a metamorphosis follows the embryonic 



development. The larvae resemble Loven's 



larva (larva of Polygordius) ; but in the 



AclurM they are characterised by a great de- 

 generation of the apical region (prseoral lobe) 



and the absence of a prjeoral band of cilia. 

 The remarkable larva known as Actino- 



trochti,, which is the young stage of the 



tubicolous genus Phoronis,* is distinguished 



by the possession of a contractile prreoral lobe, 



behind which there is a circle of ciliated ten- 

 tacles forming a collar. 



The Gephyrea are all marine. Some of 



them live in sand and ooze at considerable 



depths, also in holes in the rocks and in 



crevices between stones and corals, and in 



the shells of snails. Their food is similar to 



that of Holothurians and many tubicolous 



Annelids. 



Order 1. CH.ETIFERA = ECHIUROIDEA. 



FI&. 313. Plauariau - like 

 male of SoneUUt (after 

 Spengel). D. Intestine ; 

 WT, ciliated funnel of the 

 vas deferens (Vd), which 

 is filled with sperm. 



Gephyrea characterised by the presence, of two st.rong hooked setce 

 on the ventral side and by a terminal anus. The month is placed lit 

 the base of the prworal lobe, which is developed into a, proboscis. 



The Ecliiuroidea or chretiferous Gephyrea present no external 

 segmentation of their elongated and contractile body; they have, 

 however, in the young state the rudiments of 15 rnetanieres. This 

 * There should be a third order of Grpkyrea for these animals. 



