SEA-FISHERIES LABORATORY. 295 



The point of the axonost, even when it has pierced 

 the skin, never projects through more than a millimetre 

 or so. It is always very sharp. But the distal extremity 

 of the spine shown in fig. 9 is greatly enlarged, and 

 projects through the skin for some distance. Further, 

 its end presents a peculiar appearance, as if it were made 

 up of several spines fused together. The whole structure 

 is, however, solid homogeneous bone. The point of the 

 spine axonost has in some manner pierced the skin, and 

 has then become greatly hypertrophied. 



The point of the spine, in the normal fish, passes 

 through dense connective tissue forming the ventral wall 

 of the body cavity. In fish with hypertrophied anal 

 spines, as in the above case, there is a distinct space 

 between the spine itself and the surrounding connective 

 tissue, and this space is filled up by the tissues of the 

 tumour. These consist of a dense black ground tissue, 

 not unlike a blood clot in process of resorption, and in 

 this there are a great number of small, round bodies, which 

 are the Lymphocystis individuals. The ground tissue con- 

 sists of a mass of small cells, with large nuclei, and here 

 and there it is infiltrated by large blood vessels. This 

 tissue lies between the parasites and towards the centre of 

 the tumour round the end of the spine. The parasites 

 themselves present all the characters of Lymphocystis, as 

 described by Woodcock, so that it is unnecessary to say 

 anything about them here. 



The whole structure, tumour and anal spine, is pro- 

 bably produced in the first instance by the laceration of 

 the skin, caused by the accidental protrusion of the anal 

 spine. The lesion thus caused is then invaded by the 

 parasite, whether from within or without is uncertain. 

 The hypertrophy of the anal spine itself is most probably 

 the reaction to the parasite. 



