OVERTON : NOTES ON HELICELLA BARBARA (l.). 127 



In the absence of any detailed account of the structure of this 

 organ, Mr. Walter E. Collinge has very kindly had prepared for me a 

 series of sections, which, I think, offer evidence of the relationship of 

 this gland with the dart gland of other Helices. 



In a transverse section through the proximal end (Fig. 2), the 

 external wall is seen to be made up of a connective tissue sheath and a 

 series of circular muscle fibres, which constitute the greater portion of 

 the organ. Within this, at intervals, are groups of small gland cells 

 and a lining layer of columnar epithelial cells. The lumen in this region 

 has a somewhat stellate appearance, owing to the wall being thrown 

 into a series of large and small longitudinal ridges. Towards the middle 

 of the gland these ridges become Ipss pronounced (Fig. 3) ; otherwise a 

 transverse section through this region differs very little from the condi- 

 tion observed in Fig. 2. In a section through the distal end the gland 

 cells appear to be absent, as also any indication of the longitudinal 

 ridges, and the lumen contains a mass of mucous (Fig. 4). 



After comparing the histological structure of this gland with that 

 of other dart-glands, and, taking into consideration its position in 

 relation to the other terminal ducts of the generative organs, I am 

 inclined to regard it as a degenerate dart-gland rather than an appendix 

 or mucous gland. 



EXPLANATION OF FIGURES. 



Fig. I Helicella barbara (L. ). The terminal ducts of the generative organs. 



lleference Letters. — d.gl. Dart-gland, f.ov. Free-oviduct, ov. Oviduct. 



p. Penis, pr. Prostrate, p.m. Retractor muscle, r.d. Receptacular 



duct. V. A'agina. v.d. Vas deferens. 

 Fig. 2. Transverse section through the proximal end of the degenerate dart -gland. 



cm. Circular muscle fibres, c.t. Connective tissue, ep. Epithelium. 



g.c. Gland cells. 

 Fig. 3. Transverse section through the middle of the gland. 

 Fig. 4. Transverse section through the distal end of the gland. 



