60 W. N. F. WOODLAND 



longitudinal musculature of the body. These muscle-fibres 

 constitute the true retractor muscle of the proboscis 

 (rtm), and are very similar in form and disposition to the 

 retractor muscle-fibres of the prolwscis of a simple Turl)el- 

 larian, e.g. Pseudorhy nchus bifidus, v. Gr. The 

 terminal thickening (tt) of the proboscis consists mainly of 

 short columnar cells and forms a thin cellular pad covering 

 the anterior extremity of the huge axial muscle just referred 

 to (PI. 4, fig. 16, bm). It is to be remarked that this introvert 

 proboscis does not possess extraneous radial protractor muscles 

 attached to the body-wall. ^ 



Occupying the central axis of the proboscis is the huge muscle 

 (PI. 4, fig. 16, bm) which is so conspicuous in Amphilina and 

 which previous authors have either labelled ' retractor ' or, 

 in view of its disproportionate size to the minute proboscis 

 which it was supposed to retract, have regarded as a bundle 

 of gland ducts ! Before discussing, however, the views of 

 previous authors, I will describe the entire apparatus of the 

 proboscis. The huge muscle can be seen to extend posteriorly 

 as far back as the anterior end of the ovary (PI. 4, fig. 20), 

 its shiny fibres showing plainly in whole mounted specimens 

 of the worm. Anteriorly, i.e. in the anterior fifth of the body- 

 length, it is of considerable thickness and occupies at least the 

 middle third of the body seen in transverse section (PI. 3, 

 fig. 5), but more posteriorly it becomes attenuated (PI. 3, fig. 4) 

 and immediately in front of the ovary only consists of a few 

 centrall}^ situated fibres. Each of these fibres (some nearly 

 as long as the worm itself) can be seen, if traced through serial 

 sections, to run parallel with the central longitudinal axis 

 of the body for the greater part of its length, but just before 

 its termination it always bends at right angles (i. e. becomes 

 more or less radially disposed in a transverse section) and 

 becomes connected with one of the remark- 



^ Cohn figured extraneous radiating protractor muscles in his drawing 

 of the proboscis of A . f o 1 i a c e a , but they certainly do not exist in 

 A. paragonopora. 8alensky provides what is probably a much 

 more accurate figure and shows no extraneous muscles. 



