206 SECTIONAL ADDRESSES. 
lives at the expense (1) of formed substances, (2) of these and alga- 
products, (3) of alga-products only, and finally (4) of the alge them- 
selves. This constitutes a true evolution in a species from a free 
existence, depending only on outside sources of food supply, to a 
symbiontic mode of life, and lastly one merging into parasitism. 
(2) Symbiosis in Insects. 
Among insects we find a whole series of progressive adaptations 
toward an association with micro-organisms of different categories :— 
Group I.—The utilisation by insects of micro-organisms cultivated 
by them outside their bodies. ‘lo quote three examples: (1) The larvee 
of the beetle Xwuloteres lineatus (Bostrichide) form galleries in the 
wood of Pines. ‘The galleries have a characteristic blue colour, produced 
by the growth of the fungus Ambrosia upon their walls, the fungus 
being cultivated by the larva for food. The beetle is incapable of 
digesting cellulose. Analogous cases occur among Ants and Termites 
thus: (2) Termes perrieri of Madagascar, studied by Jumelle and Perrier 
de la Bathie (cited by Portier, 1918), builds numerous chambers and 
galleries. The termites collect dead wood, chew it up finely, swallow 
it, the wood passing unaffected through their intestine and out in the 
form of small spherical masses (0.5 mm.) which are cemented together 
as porous cakes that are impregnated with digestive secretions. Fungi 
which develop upon the cakes serve as food for the termites, and in 
well-cared-for nests the growth is harvested by the workers who triturate 
the mycelium and spores and feed the young larve therewith, whilst 
older larvee receive spores, and large larve receive mycelium and the 
triturated wood contained in the cakes. (3) A third example is that 
of ants belonging to the genus Atta which cultivate fungi over areas of 
5 to 6 square metres ; here the queen, when about to found a new colony, 
carries away a small ball of fungus in a corner of her mouth wherewith 
to start a fresh culture in the new habitat. 
Group II.—Symbiotic organisms developing in the lumen of the 
intestine and its adneza. As examples may be cited the bacteria 
occurring in the intestines of fly larvee (Musca, Calliphora, &c.), which 
aid the Jarva to digest meat; the bacteria associated with the olive-fly 
(Dacus olea); the Trychonymphids of xylophagous Termites (Leuco- 
termes lucifugus). 
Group III.—Intestinal symbionts situated in the epithelial cells of 
the digestive apparatus. The most striking instance is found in Anobium 
paniceum, a small beetle commonly occurring in flour, biscuits, dried 
vegetables, &c. In a part of its mid-gut are found cells filled with 
symbiotic yeasts undergoing multiplication (Escherich, 1900). The 
symbionts are not transmitted hereditarily but are acquired by the larva 
on hatching, being eliminated by the female beetle. 
In this connection may be mentioned with reserve the observation 
of Portier (1918) upon xylophagous Lepidoptera (Cossus, Nonagria, 
Sesia, &c.) which, according to that author, possess intestinal fungi 
(Isaria) that multiply in the gut and form spores that penetrate the 
intestinal epithelium and attain the perivisceral cavity, fat-body, and 
