ARCHIANNBLIDA. 



453 



s a 



FIG. 360. Transverse section through 

 the body of Protodrilus (after Hat- 

 schek). S, S the two ventral nerve 

 cords ; G gan^lionic layer of the 

 same ; D alimentary canal ; N ne- 

 phridiuin ; M oblique muscular 

 sheets (transverse muscles) ; Oo 

 ova. The dorsal and ventral mesen- 

 teries are shown. 



of the nerve cord to the lateral body-walls (Fig. 359), and in 

 Protodrilus the body-cavity is traversed by a sparse reticulum. 



There is a pair of simple nephridia 

 in each segment, opening internally 

 into the preceding segment ; the first 

 pair opens into the body-cavity of the 

 hinder part of the head in Protodrilus. 



The vascular system consists of a 

 dorsal vessel in the dorsal mesentery, and 

 a ventral in the ventral mesentery, and 

 of connecting vessels. The blood is 

 red, yellow, or green, or colourless. 



The generative organs are developed 

 from the coelomic epithelium, and are 

 discharged into the body-cavity. In 

 Polygordius* the ova probably escape 

 by rupture of the body -Avail, and the 

 spermatozoa by the nephridia. Proto- 

 drilus is hermaphrodite. 



The larva of Polygordius is known as Loven's larva. It is a 

 typical trochosphere (Fig. 361, a), and possesses a preoral ciliated 

 ring (Prw), a weaker postoral ring (Pow), a thickening of ectoderm on 

 the preoral lobe the apical plate, a ventral mouth, and a terminal 

 anus. There is a pair of mesoblastic bands at the hind end (Ms), 

 terminating in front in the larval kidney. This posterior part of the 

 body elongates, its mesoderm becomes segmented into somites ; and 

 it gives rise to the body of the worm (Fig. 361, b, c). Later the 

 anterior end diminishes relatively in size, and becomes the head of 

 the adult (Fig. 361, d). 



Saccocirrus Bobr. ,t should probably be placed here. It is found in the Black 

 Sea and Mediterranean in shallow water on gravel, has a long (20 to 80 mm.) 

 and narrow body with a groove on its ventral surface. The segments are 

 numerous, and each of them, except the first, carries two dorso-lateral bundles 

 of simple setae. The preoral lobe has two long tentacles and two eyes ; between 

 the preoral and postoral part (buccal segment) of the head are two ciliated pits. 

 There are no parapodia, but the lower parts of the bundles of setae are enveloped 

 in a cutaneous sheath, which can be protruded or retracted into the body. The 

 setae are enlarged and grooved at their free ends. There are two characteris- 

 tically marked appendages at the hind end, on each side of the anus, by which 



* In Protodrilus it is said that the eggs pass backwards through the meshes 

 of the body-cavity reticulum to a pore on the ventral side of the last segment 

 {Repiachoff). 



t Marion and Bobretzky, Ann. Sci. Nat. (6), 2, 1875, p. 69. 



