396 : SECTIONAL TRANSACTIONS.—D. 
SECTION D.—-ZOOLOGY. 
(For references to the publication elsewhere of communications entered in the | 
following list of transactions, see page 466.) 
Thursday, August 7. 
1. Mr. F. A. Porrs.—Intracellular Digestion in Invertebrates. 
In the protozoa, when the animal digests its own food, the process is neces- 
sarily intracelluiar. The rest of the invertebrate phyla are divided into two 
groups. In one of these there is no intracellular digestion by the cells of the 
endoderm. This includes Annelida, Arthropoda, Echinodermata, and other 
smaller phyla. In the other group, containing Porifera, Celenterata, Platy- 
helminthes, and Moilusca, some part of the endoderm is often phagocytic. There | 
is usually a preparatory extracellular digestion. In the Ceelenterata this breaks 
up the food, often consisting of comparatively large animals, into minute 
particles which are taken up by the cells of the mesenteric filament in which 
digestion is completed. In the Gastropod Molluscs, however, digestion in the 
flesh-eating forms is mainly extracellular : in the vegetarians it is largely intra- 
cellular. In such an example of the latter class as Helix the enzyme in the 
preparatory extracellular digestion is a cytase, which dissolves the walls of 
the plant cells and sets their contents free for the intracellular proteolytic diges- 
tion which follows. In other cases, besides, intracellular digestion becomes 
prominent when the diet is specialised, and particularly when it contains ele- 
ments which are normally indigestikle, such as the chloroplasts and nematocysts 
in the food of the Opisthobranchs and the wood fragments ingested by Teredo 
amongst Lamellibranch Molluscs. Thus intracellular digestion may be a mark 
of specialisation. In the Arthropods where the capacity for intracellular diges- 
tion has been lost, certain forms feed on wood in like manner to J'eredo, but 
the function of digestion is apparently performed by symbiotes—e.g. protozoa 
(Termites) and bacteria (Tipulids). 
2. Mr. D. Warp CurtiEr and Miss L. M. Crump.—Observations on 
the Growth and Reproduction Rate of a Ciliate. 
It is well known that when protozoa are inoculated into artificial culture 
media, the resulting growth is very irregular. Sometimes the organisms fail to 
increase in numbers, while on other occasions there is a rapid increase during 
the first day or two, followed by a period of rest. Usually, however, a maximum _ 
number is attained in the culture, after which the population decreases gradually, 
showing, however, considerable variations in the numbers during the process. 
The causes of this sequence of events have formed the subject of much 
research by earlier workers, but, from the results, no definite conclusions have 
been drawn. A study of the rate of reproduction of a ciliate, Colpidiwm colpoda, 
has shown that the increase of numbers follows a definite progression, provided - 
that certain factors are controlled. Thus the air supply, the nature of the 
medium, the number of organisms inoculated, and the food, are important 
external agents, while the age of the organism used for inoculation is an example 
of a factor, inherent in the animal, capable of affecting the rate of reproduction. 
The action of these modifying factors has been tested on both mass culture 
and on single ciliates. 
The supposed acceleration of reproduction which one organism produces in 
another (allelocatalysis) has also been tested, but with negative results, though 
there is evidence that the addition of small quantities of substances similar in 
nature to ‘bios’ has a marked effect. 
3. Prof. Joun Tarv.—The Mechanism of Massive Movement of the 
Operculum of Salanus nubilis. 
