PROGRESS OF MICROSCOPICAL SCIENCE. 29 



ported by stiff projecting spicula. The bottom of these pits is formed 

 by a thin membrane or diaphragm, perforated by very numerous small 

 round or oval openings, which are quite variable in size, even in the 

 same area, and in many cases are so numerous and large in the central 

 part as to be separated only by a mere network, when they become 

 polygonal. This perforated membrane is filled with minute, many- 

 rayed double-stellate spicula, with a small number of much larger 

 ones having four or five acute rays. Beneath the diaphragm the pits 

 become more or less funnel-shaped, and communicate with large round 

 anastomosing channels, which ramify through the sponge-mass. 



It seems necessary to refer this remarkable form to the genus 

 Dorvillia, and therefore he proposes to consider it a new species under 

 the name of Dorvillia echinata. 



Striated Muscular Fibre. — At a recent meeting of the Boston 

 Society of Natural History, Dr. Thomas Dwight read a paper on the 

 " Structure and Action of Striated Muscular Fibre." His studies had 

 been made on the muscles of the legs of the small water-beetle Gyrinus. 

 Their covering is quite transparent, and after the leg has been cut ofi" 

 and put into a drop of water under a covering glass, the contractions 

 can often be observed for over an hour. He found that the fibre, at 

 rest, consisted of narrow granular transverse stripes, with broad light- 

 coloured bands between them. Close to the black stripe there was a 

 glaring white reflexion, but midway between two stripes the fibre was 

 grey. When the fibre contracted the black bands came nearer together, 

 and their granular structure became more obscure; the grey band 

 disappeared, so that there was merely an alternation of black and 

 white stripes. The ends of the white stripes bulged out during con- 

 traction. As the wave of contraction moved along, it was easy to see 

 that there was no interchange of position between the black and the 

 light substances, and no homogeneous transition stage, as is maintained 

 by Merkel. When one part of the fibre is in contraction, the part 

 from which the wave is running is put upon the stretch ; the black 

 bands are divided into two rows of granules, and there is less distinc- 

 tion between the white and grey substances. 



TJie Capability of the Microscope. — According to the researches of 

 Professor Abbe, published in a late number of Max Schultze's 'Archiv,' 

 and abstracted by one of our contemporaries, it is made to appear that 

 the limit of capability of the microscope is almost reached by our best 

 microscopes, and that all hope of a deeper penetration into the material 

 constitution of things, than such microscopes now afford, must be dis- 

 missed. [I !] Experiment and theory agree in showing how the changes 

 wrought by difii-action of light passing through tine structures, whose 

 elements are so small and near each other as to call forth this pheno- 

 menon, are such as to prevent the object being imaged more geometrico. 

 Thus it may ha^jpen, on the one hand, that different structures give 

 the same microscopical image, and, on the other, that like structures 

 give different images. Consequently, while objects of the kind 

 (systems of fine lines and the like) may appear ever so distinct and 

 well marked in the microscope, we are not entitled to regard such 



