PROGRESS OF MICROSCOPICAL SCIENCE, 125 



has been protected by the sbell it covers ; now, as tliis is wanting, we 

 find the means it takes for that purpose singuLarly effective. The 

 s^iiciila in all other parts of the sj^onge have been irregularly disposed 

 on the membranes, which is a mark of the genus to which Dr. Bower- 

 bank has given the characteristic name of Hymeniacidon. But here 

 they form themselves into a regular wall, closely packed together, 

 parallel to each other, so as to jiresent a formidable array of pikes to 

 any adventurous intruder who would attack the domicile. The sarcode 

 here thickly overlays and invests it. Here are found the pores — the 

 inhalent urgans — not, however, very conspicuous, but sometimes dis- 

 tinctly seen with an inch lens. So that, instead of finding the sponge 

 in possession of an ajjparatus of attack and destruction, which has 

 been assigned to it, we see that its offensive powers, if we may so call 

 them, have been concentrated into a system of defence, to screen it 

 from assaults from without ; and that no part of the sponge has so 

 powerful an organization as this prejiared for its protection. 



Microscopic Structure of tJie Pitchstones of Arran. — This is the 

 title of an instructive paper, with a plate, in the ' Geological Magazine ' 

 (January). We do not ourselves think that the sjiecimens represent 

 anything but mineral formations, though of course we cannot very 

 ■well say, not having seen the specimens. The author (Mr. S. Allport) 

 says that a thin section, examined under the microscope with a one- 

 inch objective, is seen to consist of an amorphous glassy base, con- 

 taining numerous long, slender prisms of a green pyroxenic mineral ; 

 the latter are occasionally isolated, but generally form the axes to 

 which are attached innumerable minute jiale green crystals, arranged 

 in exq^uisitely beautiful groups ; some wonderfully like fronds of ferns, 

 others bearing the closest resemblance both in form and colour to 

 some of the microscopic fresh-water algte ; in fact, the field of view 

 apj)ears to be crowded with minute ferns, and the most elegant sprays 

 and tufts of Batrachospermum. The glassy base has a pale yellowish 

 tint in the open spaces between the groups ; but under a higher power 

 the colouring matter is resolved into a mass of translucent granules 

 and minute crystals, the latter being much smaller than the belonites 

 which form the fern-like groups. A comparison of many specimens, 

 affording gradations in size, shows clearly that all these crystalline 

 particles consist of the same pyroxenic mineral as the larger prisms 

 which form the axes. It is worthy of remark that the tufts and aggi-e- 

 gations of belonites are invariably surrounded by a border of clear 

 colourless glass. Placed between crossed prisms, the section is, if 

 possible, still more beautiful ; the tufts and sprays then appear to be 

 formed of bright gold powder on a perfectly black ground, with fine 

 brilliant dust scattered in the dark spaces between the groups. 



Tlie GregarinidcB developed from Amoebce. — The ' Lancet,' in a 

 recent number, has taken up the subject of M. E. Van Beneden's 

 paper, of which a short notice was given by us some time ago. It 

 says that the author has followed, in the case of the Gregarina 

 giganfea, the entire series of metamorphoses undergone by the masses 

 of protoplasm proceeding from the psorospermia into a fully-developed 



