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POPULAR SCIENCE REVIEW. 
in the “American Naturalist” [Oct. 1874]. It seems that the tracheary 
system is completed last of all. The first positive condition is assumed 
on the fifteenth day, and by the seventeenth it is generally entirely 
formed. The trunks arise for the most part by means of the masses 
of nuclei out of the originally solid series of cells, the terminal branches 
of the organ out of a single cell ; the hollow space between them will 
form the cavity of the trachea, while they branch out by growing 
outwards. Yet these cells may for the most part be traced back to 
the masses of nuclei, but soon, and especially within the inner of the 
bundles of primitive muscles of the thorax, they arise from an organisation of 
the histological formative elements at hand , i.e. the muscular nuclei. This re- 
markable fact does not take place without a reaction in the muscular fasci- 
culse themselves \ their sarcolerama disappears, and they deteriorate into 
fascicles of tracheae, wanting the spiral thread. All the organs which have 
tracheae intimately connected with them have the same developed in the 
last three days. The tracheae grow out in the nervous centres, in the bulb 
of the eyes, and the alimentary canal in its entire course is surrounded by a 
network of them. They are sent to the rectal papillae in great abundance 
and with a peculiar development. The dorsal vessel, also, and the entire 
muscular system, receives tracheae, and likewise the genital cavities with 
their outlets and accessory apparatus. 
Gossamer Spiders; their Work . — Dr. G. Lincecum has read a paper of 
much interest before the Smithsonian Institute [1874]. From this we 
extract the following passage : “ I once observed one of these spiders at 
work on the upper corner of an open, outside door-shutter. She was spin- 
ning gossamer, of which she was forming a balloon ; and clinging to her 
thorax was a little cluster of minute young spiders. She finished up the 
body of the balloon ; threw out the long bow lines, which were flapping and 
fluttering on the now gently increasing breeze, several minutes before she 
got all ready for the ascension. She seemed to be fixing the bottom and 
widening her hammock-shaped balloon. And now the breeze being suitable, 
she moved to the cable in the stern, severed it, and her craft bounded up- 
wards, and, soaring away northwards, was soon beyond the scope of my 
observation. I was standing near when she was preparing to cast loose the 
cable, and had thought I would arrest its flight, but it bounded away with 
such a sudden hop that I missed and it was gone.” 
The Generative Apparatus in the Gasteropoda. — In the last published 
number of the “Proceedings of the Academy of Natural Science, Phila- 
delphia,” Dr. Chapman makes the following remarks on the generative 
apparatus of Tebennophorus Carolinensis : “Various have been the interpret- 
ations offered from time to time of the generative organs of the Gasteropoda. 
Thus Cuvier considered what is now regarded as an hermaphroditic organ 
to be the ovary. Later observers regarded this hermaphroditic organ as the 
testicle, and considered what is now supposed to be an albuminous gland the 
ovary, and which Cuvier regarded as part of the testicle. With reference 
to these views, I have recently dissected the Tebennophorus Carolinensis, a 
slug found often in our environs under trees, &c., and found both ova and 
spermatozoa in the organ regarded first as simply the ovary, later as the tes- 
ticle. I take the opportunity of acknowledging the assistance afforded me 
in my dissection by Dr. Leidy’s beautiful monograph on the Gasteropoda.” 
