On the Structure q/Magelona. 151 



" tubular fibre " of the late M. Claparede) ; but, before leaving the 

 anterior region of the body, the canals glide inward and coalesce 

 into a single large median one. The whole central nervous system 

 is hypodermic. 



So far as present examination goes, the Annelida present four 

 conspicuous modifications in regard to the position of the great 

 nerve-trunks : — 



(1) Some have the trunks situated within the muscular layers, 

 or in a central hiatus between the ventral longitudinal muscles, 

 the transverse band between the latter as well as the hypoderm 

 being external. 



(2) The cords (as in Magehnn) are distinctly hypodermic in 

 position, the oblique muscles of the body-wall being attached to a 

 ti'ansverse baud above them, or to the summit or sides of the area 

 containing them. 



(3) The ti'unks may be embraced by the closely approximated 

 (almost connate) ventral or other longitudinal muscles which 

 overlap the nerve-area. 



(4) This group is formed by those in which the cords are 

 separate throughout, being 



(a) in the substauce of the ventral longitudinal muscles, 

 or {h) below or at the edge of the same muscles and within the 

 circular coat. 



The neural canals, as far as examined, occur in about thirteen 

 families. 



Tentacles. — These remarkable organs extend to about two inches, 

 but are capable of even greater elongation. They are composed 

 of cuticle, hypoderm, basement-tissue, circular and longitudinal 

 muscular coats, the latter having a raphe at each pole in transverse 

 section. Each forms a hollow contractile process furnished with a 

 series of large cylindrical papilla) along the anterior border, a 

 series of central longitudinal muscular fibres giving the latter ap- 

 pendages a sucker-action. The afferent vessel is attached to the 

 raphe next the papilias, the efferent to the raphe at the smooth 

 border. The entire organ is reproduced with considerable rapidity. 



Reproductive Organs. — The ova and spermatozoa are present in 

 each sex in great abundance in the posterior region of the body, 

 and attain perfection in summer and autumn. On the sides of 

 the body, also, peculiar convoluted organs occur in processes com- 

 posed of the cuticle, hypoderm, and basement-tissue. 



The systematic position of Magelona^ with its peculiar external 

 form and internal structure, was a source of uncertainty to Dr. 

 George Johnston, the only author who attempted its consideration 

 in this respect. So puzzled was he that he placed it (as Mcea mira- 

 bilis) at the end of his Catalogue for the British Museum, under a 

 family specially constituted for itself (viz. Mseadae). In the Cata- 

 logue of the Fauna of St. Andrews it was located between the 

 ChaetopteridcTB and the Spionidxe ; but the results of further investi- 



