Structure of Mageloiia. 453 



and it is Avaved about in a vermiform manner in all directions. 

 The facility with which the blood-vessels form, and the 

 accuracy with which the various currents keep the required 

 direction in the developing tentacles and other parts, is inter- 

 esting. The developing papillae in the growing organ first 

 appear as short pale elevations of the hypoderm, and at a 

 later stage are more acutely pointed than in the complete 

 structures. At first they are also few in number, but 

 gradually increase with the growth of the tentacle. 



While the hypodermic and cuticular tissues of the tentacle 

 are continuous with those enveloping the body generally, 

 the chitinous basement-tissue and the muscles of these 

 organs have a special arrangement. Where the tentacle 

 joins the body-wall the basement-tissue bounding the ventral 

 longitudinal muscle is specially thickened, and to this is 

 attached the basal chitinous layer of the tentacle^ by a short 

 anterior and a long posterior curve (as seen from above). 

 The special muscles of the tentacle take origin from this 

 point. Moreover, at the termination of the median cephalic 

 muscle, certain fibres of the transverse muscle, boldly marked 

 at first (and in keeping wuth those of the central muscle), 

 pass outward and backward to the base of each tentacle, 

 where they are lost. Such are probably attached to the 

 chitinous basement-tissue, and, as formerly noticed^ aid in 

 the movements of the region. 



In a large male loaded with spermatozoa the tentacles 

 ■were comparatively short and inert, and from the appeai'- 

 ance of other specimens it is possible that at the reproduc- 

 tive season degeneration of the organs may occur in s(jme 

 instances, or the animals themselves may perish. Degenera- 

 tion of the tips of the tentacles is common in confinement. 



On the whole the tentacles show a further differentiation 

 of the ciliated hypodermic groove observed in Polydora 

 cilia t a and other Spiouidje, in PhyUochcetopterus and Spio- 

 chcetopterus. The entire absence of cilia, however, demon- 

 strates that these organs are not always distinctive of a 

 respiratory function, as M, Claparede seems to think. The 

 structure of the papillne, again, would indicate that particles 

 may be passed from the one to the other, and they often 

 jerk independently. Further, in regard to the circulation of 

 the organs, the great contractility of the muscular afferent 

 vessel has an important physiological bearing, since it not 

 only sends a swift current to the tip, but through the 

 numerous capillaries which join it to the efferent. The latter 

 also possesses a rapid current, but dilates very readily, espe- 

 cially when an obstruction occurs, as in the movements of 



