April 2, 1894.] Sv/pplement to the " Tropical Agriculturist" 
715 
One method of eoming to some conclusion 
with regard to the soluble plant food in a soil is 
by analysing the drainage water. To give some 
idea of the very slight amount of matter in 
solution in drainage water, it may be mentioned 
that not more than from -04 to 'Oo per cent, is 
usually found in drainage water. Of this 
amount the most is organic matter. It is obvious 
that the amount of mineral food in drainage 
water falls far short of the actual available 
mineral food. We know well that when either 
soluble phosphoric acid or potash is added to 
the soil, they are retained in a very firm way 
by the soil particles, as is illustrated by the fact 
that when .<uch soil is treated with water the 
phosphoric acid or potash is not washed out, as 
we should expect it to be. Considerations such 
as these point to the fact that probably much 
of the available mineral food in a soil is neither 
very soluble, nor, on the other hand, very in- 
soluble. The point, therefore, to be aimed at, is 
to use some solvent which will dissolve this 
available mineral food, and not dissolve anything 
more than what is available. A weak acid solu- 
tion is what is wanted, the only difficulty being 
its strength. This Dr. Dyer ascertained, as we 
mentioned last week, by carrying out an ex- 
amination on the acidity of plant-roots. By 
transplanting this into an equivalent of citric acid, 
he found that this amounted to a 1 per cent, 
solution of citric acid. 
ZOOLOGICAL NOTES FOR AGRICULTURAL 
STUDENTS. 
Class in. Reptilia. Among the reptilians res- 
piration is aerial, never by gills ; the pulmonary 
and systemic circulations are always connected 
together, either within the heart itself, or in 
its immediate neighbourhood ; the blood is cold ; 
the skull has one condyle ; the integumentary 
covering is in the form of scales or plates 
and never in the form of feathers. 
The class includes four living orders and 
five extinct orders. The living orders are 
1. Clieloiiia (Tortoises and turtles). 
2. Ophidia (Snakes). 
3. Lacertilia (Lizards). 
4. Crocodilia (Crocodiles and alligators). 
The Chelonians are conveniently divided into 
groups according as the limbs are adopted for 
swimming, for progression, or for an amphibious 
life. The aquatic forms are well known as 
turtles, distinguished by having the carapace 
depressed, and the limbs converted into oar- 
like flippers with which the animal swims. 
The two most important of the turtles are the 
edible turtle and the hawk's bill turtle. The 
former is much used as a delicacy, and the 
latter is of commercial value for the horny 
scales which cover the carapace, and which 
are largely employed for ornamental purposes 
under tiie name of " tortoise-sliell.'' The land 
tortoises have a rounded and convi'.x; carapace 
with distinct toes furnished witli sliort claws. 
The best known species is the tcstudo groeca 
which ij sometimes kept us a domestic pet. 
The pond and river tortoises are furnished 
yith viebbed Jeet, ou4 lead 51 jemi-ac|«atic life, 
The latter have the carapace covered with a 
leathery skin, without horny scales, and are often 
called " soft tortoises." 
The order Ophidia includes most of the animals 
which would commonly be called snakes or ser- 
pents. They are generally distinguished as poison- 
ous and non-poisonous. In the harmless snakes 
the teeth are solid and are arranged in rows in 
both jaws and on the palate. In the poisonous 
snakes, on the other hand, the upper jaws 
are usually destitute of the ordinary solid 
teeth, but carry a pair of long curved •' poison- 
fangs." These fangs are pointed backwards 
when not in use, but they can be erected at 
will, by muscular action, the moment the 
animal wishes to bite. Each fang is hollow, 
and is perforated by a fine tube or canal 
opening by a distinct aperture at the point of 
the fang. The canal communicates with a 
gland jtlaced under and behind the eye, which 
secretes the poison. 
Of the members of the class Lacertilia, the 
house and garden lizards and the iguanas are 
very familar. The lizards are distinguished 
from the crocodiles in not having their teeth 
implanted in distinct sockets, and by the fact 
that the skin developes horny scales, but never 
bony plates. The crocodilia include the croco- 
diles and alligators or kaimans. They are the 
largest of existing reptiles, and are dangerous 
and voracious creatures. 
Class IV. AvES. In birds, respiration is 
aerial ; the lungs are connected with air sacs 
scattered through various parts of the body, 
serving alike to reduce the specific gravity of 
the body and to assist in the aeration of the 
blood ; the blood is warm ; the integumentaiy 
covering is in the form of feathers; the fore- 
limbs are converted into wings ; the females 
are oviparioiis ; and the skull has one condyle. 
The skeleton of tlie bird exhibits some points 
of peculiar interest. The breast bone in all 
birds which fly is furnished with a prominent 
ridge or keel to which are attached the mus- 
cles which move the wings : in birds which 
do not fly there is no keel upon the breast 
bone. The furculum, or " merry 1 bought," is 
a V. -shaped bone which keeps the wings at 
the proper distance from each other, and which 
is really composed of the united collar-bones 
or clavicles. The digits in the bird are reduced 
to a rudimentary tliumb and two fingers. There 
are no teeth in birds and the jaws are sheathed 
in bone constituting the beak. The tongue is 
usually horny but sometimes fleshy as in. 
parrots. The gullet is usually dilated in the 
lower part of the neck into a pouch called 
the "crop." From the crop the food passes 
into the " proventriculus'' or true digesting 
stomach, which opens into a muscular cavity 
called the "gizzard" which finally leads to the 
intestines. Tlie grinding action of the gizzard 
is assisted bv the gravel and small pebbles wliich 
many birds are in the habit of swallowing. 
The forni of the eyes is maintaine<l by a circle of 
bony plates : in addition to tlie ordinary eye- 
lids there is a third membranous lid (the 
membrana nictitaiis) placed on tlie inner side 
of tlio eyo and which can bo drawB over tUv froijt 
ot tbe ©ye .lilte a curtain. £ vr»- 
