grown specimens. The commonest parasites of both .classes are Copepods. The
family Brgasilidse furnishes ectoparasites which run about oh the branchiae of Dorids
and cerata of Solids. Most authors refer them to the genus Lichomolgus, but some
cite two genera, Dm-idicola and BolMcola. Hecht1 states that Lwhomolgm ioridkola
is found indifferently on Doris Meroulata, Jorurma jolmstonirTriopa claviysra, JEolSdia
papillosa, FaceUna coronata, AnUopeUa cristata and Proctonotus m-ucroniferus, varying
in coloration according to its host. Infusoria of the genus Lunophwa also frequent
both Dorids and Solids. A Pycnogonid, Nymphonparasiticum, is parasitic on
fimbriata.
The commonest internal parasites are also Copepods of the family Chondracanthidse.
The genus SplancJmotrophus Hancock is represented by five species found m British
Nudibranchs, both Dorids and Solids. ‘ The body of the Splandmotrophus is concealed
within its host (usually in the general body-cavity near the heart), but the two terminal
egg-sacs project externally. They are often not noticeable among the dorsal appendages,
but are sometimes conspicuous, as in Lomanotus genei, which appears much exposed to
the attacks of a large Splrnichnotrophus? -Dess common internal parasites are Cestodes
(Tetrartynchus sp.), Trematodes (Distomwm gland), and Nematode wopnsv-Ttojdast-
named, though apparently not recorded from British Nudibranchs, are sometimes found
in enormous quantities in tropical forms. Vegetable parasites are rare. The buccal
organs and anterior part of the body have been occasionally found to be invaded by
vegetable growths described as Phycomycetes, and the presence of symbiotic algffi in the
dorsal integuments has been suspected but not conclusively proved.3
The Nudibranchiata do not create an impression of intelligence^ and in this they
resemble most Molluscs,. except the Cephalopoda. We are perhaps apt to connect
intelligence with limbs; anything that grasps and reminds us of a hand suggests volition
and purpose. But the slimy sluggish proceedings-of these legless and-handless beasts
seem to be little more than vegetative. When a crab such as ImcMsIgt Byas plants seaweeds
and zoophytes on its back, it seems to show extraordinary intelligence or instinct.
But when an .» l id utilizes foreign bodies for (Inferior, by eating' an Actinia and turning
its stinging cells into ammunition, this seems a physiological process, strange indeed, but
as independent of volition as is digestion. But probably the difference in intelligence
between the acts of the crab and of the » l i d is not great. I t is remarkable'that such,
delicate and apparently defenceless animals as the Nudibranchs do not make burrows or
tubes like those of Annelids. The explanation must be that thanks to mucus, nematocysts,
and the other means described above, they are much better-defended thau we think. The
only recorded attempt to make a lodging for themselves is the habit of some forms
(especially Idalia) of eating into the substance of Ascidians and sponges until their
gluttony affords them a shelter. But this form of residence cannot be given a high place
in the annals of marine architecture.
1 Nearly allied are the two genera Ismailia and Briarella of Bergh, recorded from exotic
Nudibranchs.
2 Probably Spl. insole,is Scott. Ia a tropical Dorid SO mm. long I have found a Splandmotrophus
(or species of an allied genus) 10 mm. long, that is, one third the size of its host.
8 In Doridoeides by Eliot and Evans, and in Melibe by Hornell.
The most important sense-organs of Nudibranchs are probably the rhinophores or dorsal
tentacles, which are not only olfactory in the strict sense, but enable the animal to test the
quality of water and detect the presence of anything undesirable. They seem to be aware
of the presence of one another or of suitable food at a considerable distance, and probably
this information comes from the rhinophores.? The eyes can hardly id» more than distinguish
light and darkness, for though they are usually well developed they are always
covered by the dorsal skin. The sense H touch extends to the whole of the integuments,
but is specially delicate in the oral tentacles and branchiae. In some tropical Dorids these
latter are sensitive to light and will contract if a shadow falls on them. I have not found
thas '^joccur in British forms, but their branchiae are very sensitive not only to touch but
to any movementQfHie water. Otoliths (gr otoconia) are always-present in the central
nervous system, but their precise functions are not certain.
The most complicated, if not the most intelligent acts of Nudibranchs, as of most invertebrates,
are concerned with depositing (heir eggs. The precautions taken to protect or
even to hide their eggs .are not elaborate; and the propagation of the -species is ensured
chiefly by the enormous number produced. I t has been calculated that the nidamental
ribbon of Doris may contain 600,000. Sometimes the strings or- ribbons containing the
eggs are left in conspicuous positions ; sometimes they .are placed in surroundings where
they are not notioeable, or in sheltered nSbks, such as the under side of rocky ledges. But
in all cases the eggs are enclosed in some: hind of case.
At certain times of the year Nudibranchs to the coast in order to pair, and they
probably take little nourishment at this season. In ffiefueriod immediately before spawning
the stomach is found to be empty, and the genitalia, especially the mucus and albumen
glands, swell to such a size that, they compress the alimentary tract against the dorsal
integuments. 'SMBe details Ss to- the act of pairing are given by Hecht.3 It is reciprocal,
and though hermaphrodite Mollusca are incapable of self-impregnation both individuals
spawn after mating. But some species (e. g. Doris tuberculata) pair more than
once before both spawn, at any rate in captivity. The equivalent of a nest is provided by
transparent membranes of various shapes in which the eggs are enclosed. The simplest
form of egg-case is: a rounded capsule such as that laid by the Limapontiirlas. Not much
more elaborate are the oval masses of bright white which iralsina exigua hangs on seaweed,
and the kidney-shaped capsules of Tergipes despectas. Many small HUolids, such as
Amphoriiut aurcvntiaca and A. olivacea, deposit spawn in a single imperfect coil, generally
resembling a roughly drawn crescent, and the spawn of some Polycerids, such as Polycera
quadrilineata and Ancula cristata, is much the. same. But other genera, both of iEolids
and Dorids, produce more complicated patterns. In structure the spawn may be either
a simple string, or a ribbon with eggs evenly distributed, or a ribbon with the eggs
1 One would be inclined to think f l i t the efficiency of the rhinophores was due to the delioate
perfoliations with which they are often!: io v e r i ||; :: But among the iEolids genera whose rhinophores
are smooth (eigi CorypMa)!. see* inno respect fnferior | s ; their relatives who have them perfoliate
(e.'g. Facelina).
2 Hecht 1, pp. 678—681. All observers agree that the genitalia are greatly extruded in copulation,
so that the spermatotheca may act as a bursa copulatrix, difficult as this is to believe when it is
in its normal position.