56 MR. A. HANCOCK AND THE REV. A. M. NORMAN 
Doto coronata found in rock-pools at Cullercoats, on the Northumberland coast, by Mr. 
A. Hancock and Mr. H. T. Mennell, in the early part of last year. A few specimens had 
occurred some years ago on the same coast, and are mentioned in the * Monograph of the 
British Nudibranchiate Mollusca,’ at p. 26. One of these latter examples was imbedded 
in Kolis rufibranchialis, and had the ovigerous sacs, which were large and more irregular 
in form than usual, of a rose-colour and protruding in the region of the dorsal tentacles. 
This may probably prove to be a distinct species. 
'The three specimens obtained at Cullercoats had all taken up their residence immediately 
below the dorsal skin in the neighbourhood of the heart. They lay across the visceral 
chamber, resting with their under surface upon the alimentary tube and ovary, which they 
clasped with their lateral processes ; the thorax, moreover, is undoubtedly held close to these 
parts by the two pairs of hook-formed thoracic feet, while the large uncinate antenn:e lock 
the head also to the part attacked. 
As in the former species, the abdomen penetrates the skin, in this instance amidst the 
dorsal or branchial papillae. Here the ovigerous sacs, which are about as large as those 
organs, float, bathed, no doubt, by the branchial currents of the unfortunate Doto ; so 
that the eggs are thus vivified by the organie labour of the sustaining animal, as is the 
case also in the species first described. 
The two parasites forming the subject of this communication are remarkable for their 
great sizein comparison with the animals which they infest. Splanchnotrophus gracilis is 
not very much shorter than the length of the liver upon which it lies, and which it almost 
encircles with its arm-like processes ; while Splanchnotrophus brevipes nearly occupies one- 
third of the visceral cavity of Doto coronata, and lives in a position where it might be 
thought to interfere with the central organs of circulation ; and in the case of Eolis rufi- 
branchialis, before alluded to, the parasite must have been in contact with the cerebral 
ganglions. Yet these animals seemed perfectly unconscious of the presence of the 
insidious foe that was feeding upon their life's blood. They moved about apparently 
quite at their ease, and were in no way distinguishable from unafflicted individuals, 
except by the presence of the protruding ovigerous sacs of the parasite. They had mostly 
attained their full growth, and there seemed every probability of their living the usual 
time allotted to the life of the species. When they perish, the contained parasite must 
perish also; for it is an inert, helpless creature, quite incapable of any active exertion in 
search of food or for self-preser vation. No doubt, however, in the larval state it is 
endowed with the locomotive powers necessary to enable it to approach, select, and take 
up its abode in the creature most suited to its economy, where, soon losing the higher 
powers of its youthful state, never again to assume them, it becomes fixed for the remainder 
of its life. 
The parasite, lodged within the body of its selected victim, is entirely cut off from the 
aérating influence of the surrounding water, with the exception of the tip of its micro- 
scopic abdomen and the ovigerous sacs. In the male, however, no part of the animal 18 
exposed. Gills to a creature so situated could be of no use, and here it is quite impossible 
for any part of the surface of the parasite to act as their substitute. All internal parasites 
are similarly circumstanced as regards their respiration, and they, as well as the species 
