Nov. 1, 1865.] 



SCIENCE-GOSSIP. 



255 



generally become smaller as they approach the ex- 

 tremity of the body, the last spiracle being almost 

 a mere point, and without any complexity of struc- 

 ture. This order is reversed in the large water- 

 beetle {Dytiscus), for in this case, the spiracles 

 become larger as the segments of the abdomen 

 become smaller, and the last segment contains the 

 two largest spiracles. 



The large terminal spiracle (fig. 2) of the Dytiscus is 

 accurately figured in the "Micrographic Dictionary," 

 but on too small a scale to show the beauty of 

 the object. Another figure has been given in a 

 publication which obtained a wide circulation, but 

 in that figure I failed to recognise the spiracle I had 

 so frequently mounted. 



The upper and under plates of the abdomen are 

 connected by a membrane and iu this are the 



Vi^. 3. Parasite of Dytiscus. 



spiracles ; here, also, may the parasite (fig. 3), 

 which is of a red colour, be frequently found, 

 and sometimes so deeply imbedded in the skin, 

 and surrounded with a brown incrustation, that it 

 is very difficult to take one out without tearing it 

 to pieces. 



Any one who has stood beside a pond, and observed 

 the Dytiscus on the surface of the water, cannot fail 

 to have remarked, that while the heavy portion of 

 the body is immersed with the head inclined down- 

 wards, the two lighter and terminal segments are 

 above the surface. In this natural and easy position, 

 four of the largest spiracles are exposed for the re- 

 ception of the supply of air, for which, no doubt, 

 the insect rose to the surface. 



Now, if the large spiracles were in the upper seg- 

 ments it would be necessary for the insect to expose 

 its whole abdomen to the air, and this would require 

 such a continual effort as would be inconsistent with 

 the insect's ease. 



In the case of the larva of the fly, when the head 

 is buried iii the tissue it is eagerly devouring, and 

 th.e sides are bathed in the juices by which they ai-e 

 surrounded, the extremity containing the spiracles 

 freely exposed to the air. 



The above afford instances of the general con- 

 formity to system so prevalent in Nature, with those 

 deviations in minor detail which, so far from being 

 discrepancies, are among the harmonies of Creation. 



Lewis G. Mills, LL.B. 



SIMPLE OBJECTS.— VIIL 



Meadow-sweet Bkand* {Triphragmium ulmarm). 



IN a former number we gave a figure and descrip- 

 tion of a species of parasitic fungus commonly 

 found iu the autumn on the leaves of the Bramble. 

 We now direct attention to a species of Brand, which 

 is parasitic on the leaves of the Meadow-sweet 

 {SpircEa ulmaria). This is not probably so common 

 as the bramble brand, but can generally be found in 

 wet situations. The appearance which it presents 

 is that of a number of small black spots or tufts 

 on the under surface of the leaves, not larger 

 than the head of a pin. These tufts are often 

 scattered at some distance apart from each other, 

 but are occasionally closely peppered over the whole 

 under surface. When examined by a quarter of au 

 inch objective, these pustules will be found to con- 

 sist of an aggregation of three-celled spores, which 

 are formed by one transverse and one longitudinal 

 partition. The outer surface, or epispore, is studded 

 with warts or protuberances. Each spore is fur- 

 nished with a slender stipe or peduncle. It will be 

 observed that this species differs considerably iu 

 microscopical characters from the bramble brand, 

 hence botanists regard it as belonging to a different 

 genus, and one which has only this single representa- 

 tive iu Britam. To examine the present object it is 

 only necessary to remove one of the pustules on the 

 point of a sharp penknife, and transfer it to a glass 

 slide, with a drop of water or spirit, and having 

 covered it with thin glass, to submit it to a quarter 

 of an inch power. A slight pressure and sidelong 

 motion of the cover when laid on will serve to 

 separate the spores from each other. Specimens 

 may be mounted for the cabinet with balsam and 

 chloroform. M. C. C. 



* Microscopists desiring specirrtens of this brand may 

 forward stamped envelopes to W^. M. B., at tlie office of tliis 

 Journal. 



