68 W. N. F. WOODLAND 



(/) The Histology of the Body -wall and the 

 Body Musculature. 



PI. 4, fig. 2G shows the appearance of the body-wall in trans- 

 verse section. The cuticle (cut) is not very tliick, and imme- 

 diately underlying it is the thick ' subcuticula ' (subc). The 

 outer zone of the subcuticula apparently consists solely of 

 numerous radially disposed thin fibres similai' in nature to' 

 those which compose the general parenchyma. Three muscle- 

 layers lie in the outer zone of the subcuticula — the thin outer 

 circular muscle layer (ocm), a thin layer of longitudinal muscle- 

 fibres (olm), and a second thin layer of circular fibres (icm). 

 Internal to these three muscle-layers lies the inner zone of the 

 subcuticula (' epidermal ' layer), consisting of spindle-shaped 

 cells, in between which lie radially-disposed fibres and numerous 

 calcareous Ijodies (calc). Underlying the subcuticula is the 

 parenchyma (par), in the outer zone of which lies a powerful 

 longitudinal muscle-layer (ilm), and internally to which there 

 is to be seen an attenuated scattered layer of oblique longitu- 

 dinal muscle-fibres (oblm). Gland-cells (gc), excretory canals, 

 and nerve-fibres (nfi) are also of course contained in the 

 parenchyma. Included in this PI. 4, fig. 26 is a drawing of 

 a giant anchor-cell (ancc) drawn to the same scale, which will 

 give some idea as to the enormous size of this class of cell. 

 PI. 4, fig. 27 illustrates a longitudinal section through the body- 

 wall, and this shows the indentations of the cuticle and sub- 

 cuticula due to the outer substance of the body-wall being 

 ridged transversely when contracted longitudinally. 



(g) Some Stages in the Development of the 

 Larva . 



The mature eggs in the ovary which are about to enter the 

 oviduct in an Amphilina paragonopora about 30 mm. 

 long are of the ordinary alecithal type. After having been 

 fertihzed and passed through the ootype, the eggs normally 

 become encased, with a quantity of yolk material, in a relatively 

 thin irregularly oval shell, to one end of which is attached 



