220 MAGELONA. 



vertical and the lateral wall in the oblique, to the atrophied transverse on each side of 

 the ventral blood-vessel. Toward the extremity of the body, again, both become well 

 developed, the oblique spreading from the outer part of the arch over the nerve-cords 

 upward and outward in a fan-like manner to the body-wall, whilst the vertical extend 

 from the median part of the arch outward and then upward to the exterior of the dorsal 

 longitudinal muscles. 



The alimentary apparatus of Magelona consists of mouth, pharynx, proboscis, 

 oesophagus, stomach, and intestine. The buccal folds occupy a large area when the 

 proboscis is thrust out, but the buccal glands are not extruded to any extent. The 

 pharyngeal region has very prominent transverse rugae on its inner surface dorsally, and 

 is thrust into the proboscis in extreme protrusion. The proboscis forms a pinkish, 

 distensible sac, which especially in partial protrusion often presents a most regularly 

 rugose appearance, but which in complete expulsion has the form of a reddish apple 

 marked with flattened ribs, which run from the deep dimple at the apex to the base. 

 The muscular apparatus in connection with this organ is of a most complex character, so 

 that by its agency the animal can bore almost continuously forward in the moist sand, and 

 form a tunnel in which the more delicate posterior part reposes in safety. The con- 

 traction of the muscular anterior region of the body, and the relaxation of the retractor 

 muscles of the organ cause the proboscis to yield readily to the powerful stream of blood 

 that is sent against it from behindhand it smoothly unrolls outward from the transverse 

 margin of the lower lip like a supple membrane, the pinkish colour of the blood shining 

 through the translucent tissue. The extension goes on until the brownish mass of the 

 pharyngeal region approaches the front of the first body-segment and sends the muscular 

 coil into the base of the proboscis and partly under the long retractor on its way to the 

 tip — like a plug— -assisting to retain the blood therein, and giving solidity to the whole 

 organ. Thus, in its progress forward, the flattened snout is thrust amongst the sand 

 with an undulating and insinuating motion till it has advanced about its own length ; then 

 the proboscis is ejected to its full extent like an india-rubber dilator, so as to make a 

 suitable channel for the occupation of the body, while again pressing forward the 

 exploratory snout. Then all the retractile arrangements are brought into play ; the fan- 

 shaped vertical fibres pull in the basal (anterior) region, the short and long retractors act 

 on the entire organ, and the withdrawal of the pharyngeal protrusion makes an open 

 channel for the backward stream of blood which rushes into the vessels of the anterior 

 region out of the returning organ, further constricted by its own circular muscular coat. 

 These alternate protrusions and retractions are repeated at somewhat regular intervals, 

 and continued for a long time. Moreover, an explanation is perhaps afforded of the fact 

 that the annelid is partial to fine sand, seeing that the sharp fragments of coarse gravel 

 and sand might injure either snout or proboscis, though the latter is specially protected 

 by its chitinous investment. Puncture of the anterior region of the body so as to give 

 exit to the blood interferes with the protrusion of the proboscis ; indeed, it is not generally 

 thrust out after such an injury. 



The exsertile pharyngeal region is followed by a mobile part of the alimentary canal, 

 which undergoes considerable elongation when the former is thrust forward, but which is 

 variously coiled in retraction. The region lined by the chitinous investment may be 



