MAGELONA PAPILLICORNIS. 227 



Mesnil thinks that the " cirrus " is likewise present in the second region of the body, 

 dorsally and ventrally. No proof of this has yet been obtained at St. Andrews. He also 

 observes that the spike on the crown of the hook is double, and that he has only seen this 

 in the young of Nerine civratulus. 



In the posterior region of the body, in which the feet have the structure indicated in 

 Plate CI, fig. 2 c 9 a tuft of simple curved bristles occurs as a kind of support to each 

 pillar of the lateral lamellae. Moreover, a very fine tuft of slender hair-like bristles, only 

 observed on careful examination of the living animal, projects behind the pedicle of the 

 lamella. It is difficult to believe that such are the tips of the simple curved bristles, but 

 no others can be seen in the mounted preparations. Such are probably homologous with 

 the curious hidden bristles (spicular or asbestos-like) in Polydora. 



On the sides of the posterior region, from the twenty-fifth or twenty-sixth segment 

 backward, are the peculiar glandular organs (pouch-like) which occupy the lateral region 

 of each segment. 



In the first region of the body the setigerous processes are situated at the extreme 

 front of each segment ; the ninth series occupies a prominent ridge near the middle of this 

 short segment. In the posterior region the hooks are placed at first toward the anterior 

 margin of the segment, thereafter they gradually pass backward till they reach the 

 postero-lateral border of each segment. 



Hahits. — It lives in a simple straight burrow in the sand at extreme low water, but 

 it does not occur in coarse or " troubled " sand at St. Andrews. When free it can float 

 on the surface of the water. No special tube seems to be formed by the animal under 

 ordinary circumstances — simply a tunnel in the sand. If after capture it is placed in a 

 vessel with a little sand, a coating is sometimes made and in others a complete tube of 

 sand, probably to compensate for the absence of its element. 



Reproduction.— Lo Bianco (1909) gives the period of sexual maturity at Naples as 

 from December to July. Females are loaded with ova and males with sperms at St. 

 Andrews in June. 



It is remarkable that a form having a structure so complex and so peculiar should be 

 widely distributed over the globe. 



Claparede 1 (1863) describes the development of this form, his earliest stage having 

 about twenty closely arranged segments. Like many Spionid larvae it is widest anteriorly 

 and tapers to the posterior end. The cephalic region forms a wide cup with a notch 

 inferiorly, and it is richly ciliated. The first pair of setigerous processes bears long slender 

 bristles which stretch almost to the posterior end. The rest carry only a band of cilia, 

 and at each side a small pigment-spot. The alimentary canal is complete. 



In the next stage a short conical snout with two eyes appears, and two short tentacles 

 with ridges near the tip. The long first bristles are still present, but eight anterior 

 segments now have tufts of provisional bristles, whilst those behind are marked by a 

 yellowish-brown pigment-bar. 



In his latest stage the tentacles are long and coiled, and besides the basal bars have 

 long slender papillae. The short snout has four reddish eyes in a transverse row. The 

 oesophagus is differentiated by a crenated pigmented band on each side posteriorly. 

 Beobacht. Anat. Entwickl./ p. 74, Taf. x, figs. 9—14, Taf. xi, figs. 1—2. 



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