Manchester Memoirs, Vol. xlvi. (1902), No. 16. 13 



The structure of the branchial organs is less complex 

 than that of those previously described. The general 

 shape is more flattened and not so spheroidal, and the 

 hinder part is formed by a cup-shaped mass of scales 

 similar in general to those in the ocular organs, but 

 thinner and much more closely packed, so that there is 

 very little connective tissue between them (yFig. 6, p.c). 



The hollow of the cup is occupied by a central mass 

 {Fig-. 6 cut.) similar in all essential respects to that in the 

 ocular organs, except that the nuclei seem to be rather 

 more numerous and more evenly distributed. The mass 

 has the form of a very thick double convex lens ; three or 

 four nerves pass to it through apertures left between the 

 lenticular bodies forming the cup {nn.). 



In front of this central mass is a tissue composed of 

 very delicate branching fibres, rising from the surface of 

 the central mass and passing obliquely outwards. They 

 present some resemblance to the fibres constituting the 

 inner cone of the ocular organs, but, whereas these latter 

 are in general parallel to the surface of the organ, the 

 former are nearly perpendicular to it (/.;;/.). 



IV. The Abdoinmal Organs are in two groups: — A 

 set of three lying transversely in the mantle cavity {^Fig. i. 

 a 7, .?, j) close to the anterior margin of the nidamental 

 gland, the centre one being about 07 mm. in diameter 

 and somewhat larger than the lateral ones, and two 

 lying one in front of the other in the posterior end of the 

 mantle cavity in the middle line {a 4., 5). These are 

 rather smaller than the lateral ones of the two above 

 mentioned. The sections of these organs were badly 

 broken, doubtless owing to the defective preservation of 

 tbe specimen, so that it is impossible to give a complete 

 account of their structure. I was able, however, from a 

 careful examination of the fragments to satisfy myself that 



