JUNE 13, 1884. ] 
the operations of planning, making, lettering, dimen- 
sioning, altering, blue-printing, indexing, and preserv- 
ing drawings, are reduced to a systematic procedure. 
The remaining papers, for which, however, but 
little time remained, were: ‘Cross-sectioning with 
the right-line pen,’ J. B. Webb; ‘Comparison of 
three modern types of indicators,’ G. H. Barrus; ‘A 
positive speed-indicator,’ O. Smith; ‘ The experimen- 
tal steel-works at Wyandotte,’ W. F. Durfee; ‘ Early 
history of the steel-works at Troy,’ R. W. Hunt; 
‘Experiments on non-conducting coverings for steam- 
pipes,’ J. M. Ordway and C. J. H. Woodbury. 
Professor Webb’s paper referred to methods in use 
in his drawing-classes, with specimen of work. 
Mr. Barrus gave the weights of the parts of the in- 
dicators, but neglected their moments of inertia: he 
compared the general appearance of the diagrams, 
and the correctness of the parallel motions: the 
errors of the springs were given, and the action of the 
drum mechanism discussed by means of an apparatus 
for detecting changes of phase. Some of these ex- 
periments seem to be in the right direction, but no 
discussion of underlying mechanical principles was 
attempted. Mr. Smith’s machine is a counter for 
revolving shafts, with a clock which throws it in gear 
for one minute. The other papers will be read and 
discussed at the annual November meeting in New- 
York City. 
Thursday was devoted to an excursion, by rail, up 
the Alleghany River for the purpose of visiting vari- 
ous works and furnaces. Among these were the 
Spang steel and iron company’s works, the Isabella 
furnaces, the National soda-works, and the Plate- 
glass works, using natural gas asa fuel. A subscrip- 
tion dinner on Thursday evening, and a water excur- 
sion up the Monongahela on Friday, completed the 
programme of this meeting of the society. 
DEVELOPMENT OF THE THYROID AND 
THYMUS GLANDS AND THE TONGUE. 
UNDER the wide title of ‘Ueber die derivate der 
embryonalen schlundbogen und schlundspalten bei 
saugethieren’ (Arch. mikr. anat., xxii. 271), G. Born 
discusses the development of these organs as deter- 
mined by observations on pig embryos. These valu- 
able researches give us, for the first time, an under- 
standing of the morphology of the two glands of the 
above title, which have been a long-standing puzzle 
to comparative anatomists. 
The tongue arises from the anterior part of the 
ventral floor of the pharynx. The space between the 
ventral ends of the first and second visceral arches 
is at first depressed ; but later a longitudinal ridge 
grows up, separated on each side, by a groove, from 
the arches. The anterior portion of this ridge grows 
out, and becomes the free part of the tongue: the pos- 
terior part of the ridge projects between the third 
and fourth arches, and develops into the epiglottis. 
It will thus be evident that the tongue does not ex- 
tend back beyond the secondarch. After the embryo 
(pig) reaches a length of fifteen millimetres, the 
SCIENCE. 125 
tongue grows rapidly forward. (Although it has long 
been known that the tongue arises froin the floor of 
the pharynx, the evident conclusion has not been 
sufficiently recognized, that the epithelial covering of 
the tongue is entodermal, and not ectodermal, and 
therefore not the same as the lining of the mouth, as 
a continuation of which the lingual epithelium is 
customarily described. ) 
The fate of the visceral clefts has been more fully 
elucidated than heretofore. The first becomes the 
outer and middle ear and the Eustachian tube, as is 
well known: the fate of the others has been obscure. 
According to Born, the second entirely disappears, 
becoming first a closed sac, and finally undergoing 
complete atrophy; the third likewise becomes a closed 
sac, which remains some time connected with the epi- 
dermis; from the inner end of the cleft arises a short 
caecum, extending ventrally inwards and forwards, 
which is the anlage of the thymus, and is retained 
and enlarged, while the rest of the cleft is atrophied; 
the fourth cleft also remains in part as a closed sac, 
which later joins in the formation of the thyroid 
gland. 
The thymus was first shown by Kolliker (Entwicke- 
lungsgeschichte, 2te aufl.) to be an epithelial organ, 
and probably derived from a gill-cleft. Born traces 
its origin from the third cleft, as a ventral evagina- 
tion near the inner opening. The caecum grows, at 
first, without altering its position or general appear- 
ance; but the rest of the cleft is reduced to a small 
canal, the outer part, indeed, to a solid cord of cells 
(embryo pigs of about sixteen millimetres). The 
whole, except the thymus portion, is atrophied, but 
the outer cords persist for atime. The thymus anlage 
spreads out into a canal, with walls of fine, many- 
layered epithelium. The lower end of the canal rests 
against the pericardium, where the aorta makes its 
exit. In embryos of two centimetres, the lumen of 
the canal has disappeared, and from the solid cord 
many branches have grown out, most abundantly at 
the heart end. 
The thyroid gland, as was first shown by W. Miiller 
(Jenaische zeitschr., vi. 428, 1871), has a double origin. 
Born shows that the principal division arises as a 
median invagination in the floor of the pharynx, on 
a line with the front edge of the second visceral cleft. 
Very early this invagination separates from the pha- 
ryngeal epithelium, expands laterally chiefly, changes 
to a network, and at the same time moves backward 
until it comes to lie behind the glottis. Until the em- 
bryo is two centimetres long, the thyroid mass lies 
near the origin of the third aortic arch (common 
carotid); but in older embryos the division of the 
carotids has moved back, away from the head and 
the thyroid gland. The secondary portion of the 
thyroid is derived from the paired remnants of the 
fourth clefts. The median portion of the thyroid 
early changes into a network of epithelial cords. The 
outer cells of the cords are cylindrical: the inner 
cells, in several layers, are not very distinct from one 
another. Around the cords, the mesoderm forms 
sheaths of spindle cells, while between them the 
blood-vessels appear. The lateral anlagen become 
