426 
POPULAR SCIENCE REVIEW. 
Sub-cutaneous Orifices in the Head of the Eel and Conger. —JAnny com- 
parative anatomists have been puzzled to know the relations of the sense 
capsules in fishes, and perhaps there are none of more interest than those 
of Dr. McDonnel, of Dublin, on the lateral line in these animals. A recent 
investigator, the Rev. W. Houghton, adds his quota to the mass of evi- 
dence already existing on this subject. While engaged in the dissection 
of eels and congers he observed the constant presence of two sub -triangular 
openings in the fleshy portion of the head, at the point of union of cranium 
and spinal column. These he at first supposed to be special auditory 
organs, but he now leaves the question for the decision of other anatomists. 
He denies the assertion contained in Mr. PenneTs treatise, that these fish 
have an external auditory aperture in the head ; and then goes on to 
describe the orifices which he observed. Upon placing a bristle in each of 
these openings, it was found to traverse a closed-in duct in the cranium, 
and to make its exit just above the orbital bone. These tubes have no 
connection with either the vestibular sacs or the auditory nerves. He 
believes these canals to be connected with the so-called mucous system, but 
in what manner he is not aware. — Vide Pamphlet , reprinted from Quarterly 
Journal of Microscopical Science , January, 1864. 
Homologies of Insects and Crustaceoe. — Mr. Dana has constructed a very- 
simple diagram showing the nature of the homological relationship be- 
tween decapods and insects. By glancing at the sketch accompanying 
his memoir, it will be apparent that the following conclusions, at which 
the author has arrived, are correct : — ( 1 ) The insect wants the three pos- 
terior segments of the crustacean. (2) The head and thorax of the insect 
embrace the same number of segments as the head alone of the decapod. 
(3) The head and thorax of the insect contain half of its entire number of 
segments (eighteen) ; the head and thorax of the decapod contain two- 
thirds of the whole (entire number twenty-one). (4) The head of an 
insect contains six segments, which is one-third of the whole number ; 
that of a decapod nine segments or three- sevenths of the whole. (5) The 
segments connected with the organs of digestion are the tenth, eleventh, 
twelfth, thirteenth, and fourteenth in both insect and decapod. But in the 
insect the tenth is the first behind the thorax ; and in the crustacean it is 
the first behind the head. It is very questionable whether Mr. Dana is 
correct in assuming the presence of the three anterior segments in the 
insect as distinct parts. If we suppose them to be present, the difficulty 
of showing the homologies is much diminished. — See the Annals of Natural 
History for January. 
Structure of the Animal Substance of Dijfiugia. — In Mr. Carter’s memoir 
on the fresh-water rhizopods of England and India, which appeared in a 
late number of the Annals of Natural History , the author describes the 
appearances seen with the microscope when the test and animal of Difflugia 
compressa were crushed under a glass cover. The animal-matter consists 
of protoplasm embedding, small brown cells, oil globules, starch granules, 
and reproductive cells. The first are globular in form, about the -b-oVtt °f 
an inch in diameter, and appear to give the creature its light brown 
colour. The second are more alundant, vary in size, and under the 
