1888.] WORM OF THE GENUS ^OLOSOMA. 217 



termed ^. variegatnm leaJs me to believe that the individuals 

 from the Society's Gardens belong to a distinct species ; the fact 

 also that the first nephridium is situated in the first setigerous 

 segment, distinguishes my species from jE. varieyatum. I may 

 fairly lay stress upon this point of difference, as it furnishes a useful 

 character in distinguishing the remaining species of the genus. 

 Leydig's observations upon J^. niveum support Vejdovsky's belief 

 that this species may be identical with his J^. variegatum, as in 

 both there are no nepliridia in the oesophageal region. 



The accompanying drawing (Plate XII. fig. 2) shows all the remain- 

 m-r points in the structure of ^Eolosoma to whicb I wish to direct 

 attention. The cavity of the prostomium is traversed by numerous 

 unicellular muscular fibres, which, when seen on a dorsal or ventral 

 view of the animal, have the appearance of being frayed out at their 

 point of insertion on to the body-wall, forming a star-like figure '. 

 Besides these, the head-cavity is partly occupied by a network 

 formed by the anastomosis of similar fibres, as in Dinophilus ', &c. ; 

 elsewhere the ccelom is only traversed by the unicellular fibres. 

 Beneath the epidermis there is a single row of circular musculnr 

 fibres, which is continued over the pharynx. Beneath the circular 

 fibres is a single row of longitudinal fibres of a somewhat greater 

 thickness than the last ; these do not appear to be continued over 

 the pharynx. 



The nerve-ganglion is half cellular and half fibrous (fig. 2, n) ; 

 it appears to be wholly cellular in other species. 



The number and disposition of the nephridia appear to me sufficient 

 to distinguish this species, which I have great pleasure in asso- 

 ciating with the name of my friend Mr. F. W. Headley, Assistant 

 Master at Haileybury College. 



EXPLANATION OF PLATE XII. 



Fig. 1. Molosoma headhyi, higblj- magnified, from the rentral aspect. 



2. Longitudinal section tbrougli prostomium and first segments. 



3. Section through seta-sac. 



4. Section to show nephridial funnel. 



5. 6. Transverse and longitudinal sections through intestine. 



7. Cihated cells from intestine, highly magnified, to show striate free 



border. 



8. Granular masses, colourless or yellow, contained in epidermis cells of 



prostomium. 



Reference Letters. 



hi. Blood-space, v.v. Ventral blood-TCssel. n. Nerve-ganglion, m. Longi- 

 tudinal muscular fibres. »i'. Transverse muscular fibres, f/i. Epidermis, nep. 

 Nephridia. o. External orifice of nephridia. /. Funnel of nephridia. c. In- 

 tracoelomic muscular bands. «. Set«. s'. Seta-sac. sm. Band of muscles 

 uniting two seta-bundles, ph. Pharynx. 



' Cf. Vejdovskv, SB. bohm. Gesells. &c. fig. 3. 

 - Weldon, Q. J. Micr. Sci. 188(5. 



