(j6 Proceed! ))(]■■< of llic Roijcl Society of Victoria. 



be dissected out from the miderlying tissues with great ease. 

 These walls are membranous and fairly tough, and they are 

 continued from the oscular tube along its various larger 

 branches as a distinct lining membrane. 



The wall of the oscular tube is seen in transverse section 

 to be made up of the following layers, from within outwards ; 

 (a) Furthest from the lumen of the tube, a thick, rather 

 irregular layer of very much vacuolated, gelatinous tissue ; 

 (l)) A much thinner layer of deeyjly staining, fibrous tissue, 

 in which the filjres are closely packed and arranged circularly 

 around the oscular tul)e. (c) A continuous layer, only about 

 one cell thick, of cj^stenchyme. 



I have no doubt that the wall of the oscular tube is 

 completed on the inside by a delicate, flattened epithelium, 

 but I have not succeeded in demonstrating its presence. 



(2) The walls of the embr^'o-containing cavities. — What- 

 ever view may be adopted as to the relationship of the 

 embryo-containing cavities to the exhalant canal system, 

 it will be convenient to describe the structure of their walls 

 in this place. 



The only ovum which I have observed, previous to the 

 commencement of segmentation, lies in a small cavity about 

 0"1 mm. in diameter, situate in the innermost part of the 

 gelatinous laj-er of the wall of an oscular tube. Tliis cavity 

 has a special wall composed of flbrous tissue, with elongated 

 nuclei. I have not detected any lining epithelium, although 

 some of the nuclei observable may possibly belong to a 

 delicate epithelial la3^er. 



The large embryo-containing capsules are doubtless 

 developed b}' growth of the small ovum-containing capsules. 

 The walls of the large capsules are, however, very much 

 more highly developed, and consist of two very distinct 

 layers: — (a) A fibrous layer, and (/>) a lining epithelium. 

 The fibrous layer is very dense next to the lining epithelium, 

 but further in it becomes looser, and is broken into by large 

 lacunar spaces. It is composed of circularly arranged fibres, 

 each consisting of a greatly elongated, fusiform, granular cell, 

 with a deeply-staining, oval nucleus in tlie centre. The 

 fibres are so densely packed in the outer part of the layer, 

 next to the lining epithelium, that the outlines of the 

 individual cells can no longer be distinguished ; but further 

 in the cells lie further apart, and the tissue partakes more of 

 the nature of a compact, stellate mesoderm. 



