Manchester Memoirs, Vol. xlvi. (1902), No. 16. 1 1 



in form, the antero-posterior diameter being the largest 

 and measuring about i mm. in length. 



In the greater part of its structure the siphonal organ 

 is quite similar to the ocular organs. The only important 

 exception is that over the front of the anterior cap 

 a layer of very remarkable tissue is placed. This con- 

 sists of rather strong anastomosing fibres, which stain much 

 less deeply than the scales. Near the periphery of the 

 anterior cap {Fig. 5,/.) arise similar fibres which pass 



-/ 



Pis- 5- 

 Half of the fibrous mass covering the front of the siphonal 

 organ; /, mass of anastomosing arborescent fibres ; i.s., half 

 the triangular space between the two sets of fibres. 



upwards and inwards, ramifying and anastomosing as they 

 go, forming a layer nearly three times as thick as the 

 layer of scales in the anterior cap. There are thus formed 

 in section two arborescent masses, and in the triangular 

 space between them the fibres appear to be somewhat more 

 slender, more irregular, and more.deeply stained {Fig 5, t.s?). 

 On that side of the part of the organ, which is directed 

 towards the posterior end of the animal, this tissue gives 

 place to a somewhat different form. This consists of 

 wavy fibres parallel with each other and, roughly speak- 

 ing, with the axis of the organ. They are somewhat more 

 deeply stained and of a more bluish tinge than the 



