280 



POLYCHAETA 



worked out by Agassiz 1 they were placed in different genera. The 

 male zooid lias thus come to be known as Polybostrichus (Fig. 149, 

 B). It has three tentacles and two bifid palps ; there are two 

 pairs of peristomial cirri ; the testes are confined to the four 

 anterior segments, which are without natatory chaetae. The 

 female is termed Sacconereis, owing to the possession of a great 



FIG. 149. Myrianida fas- 

 data. (From Malaquin.) 

 The bright red markings 

 of the living aniolal are 

 here represented black. 

 A, An asexual individual 

 which lias produced by 

 budding from the zone (z) a 

 chain of twenty-nine zooids, 

 the oldest being labelled 

 1, the youngest 29. B, A 

 ripe male zooid (Polybostri- 

 chus), with three tentacles 

 and a pair of forked palps 

 (p). There are five un- 

 altered anterior segments. 

 C, A ripe female zooid 

 (Sacconereis) with the palps 

 fused with the prosto- 

 mium ; s, the ventral brood 

 pouch projecting on each 

 side ; t, tentacles. 



ventral brood sac ; its head possesses no separate palps ; the 

 peristomium carries only one cirrus on each side ; ova occur in 

 every segment of the body, and may even extend into the 

 hinder segments of the asexual zooid (Fig. 149, C). 



A further development of this process of gemmiparity is 

 exhibited by Myrianida. Here, there is no conversion of the 

 hinder segments, but the normal preanal zone of proliferation 

 gives rise to a large number of new segments. After a time the 

 most anterior of these becomes a head, and thus a new zooid 

 1 Alex. Agassiz, Boston J. Nat. Hist. vii. 1863, p. 384. 



