PROGRESS OF MICROSCOPICAL SCIENCE. 
97 
small opening. A few ForaminifersB were also met with, and two or 
three specimens of what appeared to be a minute bivalve shell. Be- 
sides these elements, evidently derived from living beings, the sand 
contained small black particles, which the microscope showed to be 
formed principally of crystals of augite, nepheline, and magnetic 
oxide of iron, imbedded in a glassy matrix. These were undoubtedly 
volcanic sands. The structure of these grains fully, I think, explains 
the reason why sound is emitted when they are set in motion. The 
friction against each other causes vibrations in their substance, and 
consequently in the sides of the cavities they contain ; and these 
vibrations being communicated to the air in the cavities, under the 
most favourable conditions for producing sound, the result is the loud 
noise which is caused when any large mass of sand is set in motion. 
We have, in fact, millions upon millions of resonant cavities, each 
giving out sound which may well swell up to resemble a peal of 
thunder, with which it has been compared ; and the comparison — I 
know from others who have heard it — is not exaggerated. The effect 
of rain in preventing the sound is owing to the cavities in the sand 
becoming filled with water, and thus rendered incapable of originating 
vibrations." 
A Figure of Bathyhius is given by Professor Toula in a description 
he has supplied of the results and instruments of the sea-exploring 
expedition of Sir W. Thompson. He has also described some of the 
Foraminifera. It is to be found in the Annals of the Society of Vienna 
for the diffusion of Science. 
The Development of the Salpa. — This subject has been worked out 
by Professor Todaro, of Eome, who has presented to the Eoman 
Academy a paper on the organs of generation of the Salpa. He comes 
to the conclusion that the Salpae are developed according to the type 
of vertebrates, being in part like the frogs, in part like birds, and 
in part like mammals. He says that they represent the trunk of the 
genealogical tree of the first great division of the animal kingdom. 
TJie Tunicata of the Adriatic have been studied by Professor 
Heller, who has published an essay on the subject. He describes the 
internal and external structure of the simple ascidians of this sea. 
Ascidia involuta constitutes a new species. Its body is encrusted with 
a thick layer of sand, from which only the siphons can be seen pro- 
jecting. A. reptaris is, on the contrary, a naked and transparent 
body, in the midst of which one can distinguish with ease the rami- 
fications of the interior vessels. 
The Organ of Hearing in the Heteropoda. — An important memoir 
on this subject has been written by Professor Ausserer. It will be 
found in last year's volume of ^ Annales de Genes.' 
A New Parasite has been described before the Society of National 
Sciences of Pisa by Professor Baraldi. It is the nymph of an^acarite 
Hypodectes carpophagce. This new species has been found in the 
subcutaneous connective tissue of the pectoral region of Carpophaga 
perspicillata, which died recently at the Acclimatization Gardens of 
Turin. 
