248 Proceedings of the Royal Physical Society. 
thus we notice that the habitat of the Copepod under dis- 
cussion is exceptional in two ways—firstly, in being more endo- 
parasitic than is usually the case in this order; and secondly, 
in being situated on the male reproductive duct, a fact which 
is to be compared with that of certain Cryptoniscide among 
the Isopoda, as Giard and others have shown, which seriously 
affect the male reproductive organs of their hosts. 
The connection between this Copepod and the vas deferens 
of its host is an extremely close and intimate one; so much 
is this the case, that it is difficult to fix their respective 
limits. JI have had some difficulty in preserving these 
parasites—a difficulty which has been experienced, but not 
overcome, by previous workers at this family of Copepoda. 
I find that methylated spirit is preferable to formalin; but 
the former must be added in a very gradual percentage. 
The Area affected by Parasitism—In one case the area 
affected by the attacks of this parasite was slightly over 40 
millimetres in length by 10 millimetres in breadth. In 
another case the area affected was not nearly so extensive ; 
but in the latter case the vas deferens appeared to have been 
ruptured; this rupturing might partly be the result of rough 
treatment in the trawl, or during carriage, as specimens are 
not infrequently mangled in this way. In this second case, 
the area affected only extended over 15 millimetres in length 
by 5 millimetres in breadth. 
Size of the Animal._—In one case the length of the female 
appeared to be slightly less than 8 millimetres, while the 
length of the male was approximately 5 millimetres; but the 
measurements of the female were not very exact, as it 
was difficult to fix the exact limits of the animal. We may 
notice, however, that there is not so marked a difference 
in size between the male and female of this species as in 
a number of other dimorphic Copepoda. 
Description of the Female.—The female of the older speci- 
men was evidently so much altered in form by its endo- 
parasitic habit, as to afford little or no clue as to the original 
shape of the animal. The younger stage, however, showed 
that this is one of those bizarre species deformed by warty 
outgrowths of the body. Some of these outgrowths are so 
