PROGRESS OF MICROSCOPICAL SCIENCE. 
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tions upon many mammals, reptiles, and fislies lead me to the following 
general conclusions as to the development of teeth : 
“ (i.) All tooth-germs whatever consist, in the first instance, of two 
parts, and two alone — the dentine papilla and the enamel organ. 
“ (ii.) The existence of an enamel organ is wholly independent of 
the presence or absence of enamel upon the teeth. Examples of this 
have been recorded by Professor Turner and by myself among mam- 
malia, and by myself among reptiles and fishes. 
“(iii.) Nothing justifies the arbitrary division into ‘papillary,’ 
‘ follicular,’ and ‘ eruptive ’ stages ; nor does any open primitive dental 
groove or fissure exist in any animal examined. 
“ (iv.) In all cases an active ingrowth of a process of the oral epi- 
thelium, dipping inwards into solid tissue, is the first thing distin- 
guishable, although the formation of a dentine papilla opposite to its 
deepest extremity goes on pari passu with the development of its caecal 
end into an enamel organ. 
“ (v.) A special capsule, or follicle, to the tooth-germ may or may 
not be present. When present it is, in part, a secondary development 
from the base of the dentine papilla ; in part a mere condensation of 
surrounding tissue.” 
Filaria in the House-fly. — Professor Leidy (of U.S.A.) has recently 
found that the common house-fly is afflicted by a thread-worm, about 
a line in length, which takes up its abode in the proboscis of the fly. 
From one to three worms occurred in about one fly in five. This 
parasite was first discovered in the house-fly of India, by Carter, who 
described it under the name of Filaria muscce, and suggested that it 
might be the source of the Guinea-worm in man. 
Mode of Development in Echinoderms. — Mr. A. S. Packard, jun., who 
has published an interesting summary on the development of Eadiata, 
in the ‘ American Naturalist ’ (April, 1875), draws the following con- 
clusions as to the Echinoderms : 
“ Echinoderms as a rule, then, are reproduced alone by eggs and 
sperm-cells. After fertilization of the egg they pass through : 
“ 1. Morula stage. 
“ 2. Gastrula stage. 
“ 3. A larval, temporary stage (Pluteus, Brachiolaria, Auricularia). 
“ 4. The Echinoderm grows from a water tube of the larva, finally 
absorbing the latter, whose form is often materially changed during the 
process. It thus undergoes a true metamorphosis, in a degree com- 
parable with that of some insects.” 
The Colouring Matter of Birds’ Eggs. — Mr. H. C. Sorby, F.R.S., 
our President, read a paper before the Zoological Society of London, 
May 4, “ On the Colouring Matter of the Shells of Birds’ Eggs, 
as studied by the Spectrum Method,” in which he showed that all their 
different tints are due to a variable mixture of seven well-marked 
colouring matters. Hitherto the greater part of these had not been 
found elsewhere. The principal red colouring matter was connected 
with the haemoglobin of blood, and the two blue colouring matters 
were probably related to bile-pigments ; but in both cases it was only 
