54 MR. A. HANCOCK AND THE REV. A. M. NORMAN 
processes. The under surface of the parasite is pressed to the liver, the anterior ex- 
tremity forward, but the posterior extending as far back as the region of the branchial 
circle; here the two last segments of the body penetrate the skin of the Nudibranch, to 
which they are firmly attached, so that the parasite becomes thus fixed in its position. 
Itis a remarkable fact that this penetration and attachment always take place within the 
branchial circle; and consequently the ovigerous sacs must float amidst the plumes, and 
be always exposed to the constant flow of water brought thither by the branchial cilia, 
The males are found only in those mollusks in which the females have taken up their 
abode ; and generally several of the former are associated with a single example of the 
latter: as many as a dozen are occasionally thus found with the female, though more 
generally three or four, and sometimes only one or two. They always live immediately 
beneath the skin, either adhering to the viscera (usually the liver-mass, consisting of the 
ovary and liver) or to the female, close to the vaginal openings of the first abdominal 
articulation. It is from these facts, and more especially from the circumstance of its 
frequent attachment to the body of the female, as is the case with the males of Chondra- 
ecanthus, Lerneonema, Brachiella, Ancorella, Lerneopoda, and other allied genera, that 
this animal is assumed to be the male of the present species. The characters of its 
antenne, oral organs, foot-jaws, and thoracic feet (all of which, as before shown, closely 
resemble those organs in the female) strongly corroborate this opinion; .and this simili- 
tude of parts could scarcely have been expected in such dissimilar animals on any other 
hypothesis. That they are males seems, moreover, to be established by the fact that, 
although between thirty and forty individuals have been examined, not one possessed 
ovigerous sacs or presented any appearance of such sacs having ever existed, whilst in 
every instance those organs which we take to be the male intromittent apparatus were 
present. ' 
The startling fact of these individuals being furnished with an eye appears to bear upon 
this question. It is very extraordinary that we should meet with a visual organ in an 
internal parasite; and its presence in this case is an assurance that some peculiar neces- 
sity demands its existence. 
The male lives free within the visceral cavity of the animal it inhabits, and un- 
doubtedly enjoys a limited degree of locomotion. The thoracic feet, which are well placed 
for such a purpose, are therefore relatively larger than those of the female, in which they 
seem merely to assist in holding the parasite in its proper position. The male, being thus 
endowed with the power of transferring itself from place to place, might be liable to wander 
among the viscera into the interior of the body. It is required, however, to remain on the 
surface of the visceral organs, immediately beneath the skin, where the female resides per- 
manently attached, and where the male is therefore required to exercise its sexual func- 
tion. An eye is therefore given to it, which, though extremely low in structure, is sufi- 
cient for the perception of light, which is all that is necessary to enable the creature to 
retain its position on the surface of the viscera immediately below the skin. That the 
skin possesses the requisite degree of transparency for this purpose is proved by the fact 
that the comparatively highly organized eyes of the Doris itself are placed beneath the 
dermal envelope. : 
