448 Microscopical Society, 



it unites in the centre of its area. This new membrane is at first clear and pellucid, 

 but after a short time minute vesicles, molecules andcytoblasts appear in various parts 

 of the surface, together with small patches of minute vascular tissue. These spherical 

 cells gradually increase in size, assuming the form of collapsed vesicles. As their num- 

 ber increases, their outlines become indistinct, until at length they form an even pav- 

 ing of closely compressed tessellated cells. Layer after layer of this tissue follow each 

 other, one above the other, until the whole space of the wound is completely filled 

 up. The progress of the minute primary vessels also affords an exceedingly interest- 

 ing study of the origin of vascular tissue, whether simple, branched or anastomosing, 

 not only in animals of a low degree of organization, but also in the higher warm-blood- 

 ed animals, as the author had also observed similar appearances amid the cartilaginous 

 fibres of the prepared foetal skull of an infant, and also in the somewhat similar carti- 

 laginous structure of bone in a ease of mollities osseum, described by Mr. S. Solly, of 

 St. Thomas's hospital. The remaining part of the paper was devoted to a minute de- 

 scription of the appearance of this primary vascular tissue in various stages of its de- 

 velopment in the periostracum of the shell. 



December 20, 1843.— Edwin J. Quekett, Esq., F.L.S., in the chair. 



Read, a communication from Mr. Tulk, upon certain parasites in the dog. These 

 parasites were found by Mr. Topping, on examining microscopically the contents of 

 the pustules in a mangy dog. They belong to the genus Demodea (Owen), first disco- 

 vered, figured and described by Dr. Lemon of Berlin, as inhabiting the sebaceous sacs 

 and hair-follicles of the human skin. The insects now described as existing in the 

 dog, were found in such abundance that thirty or forty were frequently seen in a sin- 

 gle drop of pus. They differ very slightly from the human parasites before referred 

 to, but analogy would lead to the conclusion that they are of a different species. The 

 discovery of this parasite may throw some light upon the causes of the disease called 

 mange, a distemper by no means confined to one class of animals ; while, at the same 

 time, it is far from being certain, whether this insect is the exciting cause, or is mere- 

 ly developed during the progress of that disorder. 



The chairman made some observations upon Tettigonia septemdecim, a North- 

 American insect sent by Professor Bailey, the ovipositor of which, he stated, forms a 

 curious microscopical object. He exhibited specimens of the male and female insect, 

 and also some wood, illustrating the injury done by it. The chairman also laid be- 

 fore the Society some earth from Petersburg, in Virginia, described by Professor Ro- 

 gers, containing fossil animalcules, and noticed several new forms found in it. 



Mr. Ross communicated an interesting observation relative to the Daguerreotype 

 process, first noticed by R. H. Solly, Esq. If an ordinary Daguerreotype portrait he 

 examined with a power of about 200 linear, the surface in the parts upon which the 

 light has acted, instead of being perfectly smooth, is found to be covered with a series 

 of minute dots or globules, arranged in a hexagonal form. Mr. Ross exhibited this 

 curious appearance in the course of the evening. 



A fluid for cleaning glass was also laid before the Society. It consists of a strong 

 solution of nut-galls ; glass wiped with this fluid is effectually freed from all greasiness. 



Mr. Busk exhibited the achromatic object-glass of a telescope, having a minute 

 Conferva growing between the lenses composing it. Some discussion took place as to 

 whether this appearance was really the effect of vegetation, or produced by a species 

 of crystallization on the surface of the glass. — /. W 



