Mr. Erasmus Wilson on the Entozoon folliculorum. 369 



While engaged in researches on the minute anatomy of the skin 

 and its subsidiary organs, and particularly on the microscopical com- 

 position of the sebaceous substance, the author learned that Dr. 

 Gustow Simon of Berlin had discovered an animalcule which inha- 

 bits the hair follicles of the human integument, and of which a de- 

 scription was published in a memoir contained in the first Number 

 of Midler's Archiv for 1842. Of this memoir the author gives a 

 translation at full length. He then states that, after careful search, 

 he at length succeeded in finding the parasitic animals in question, 

 and proceeded to investigate more fully and minutely than Dr. Simon 

 had done the details of their structure, and the circumstances of their 

 origin and developement. They exist in the sebaceous follicles of 

 almost every individual, but are found more especially in those per- 

 sons who possess a torpid skin ; they increase in number during 

 sickness, so as in general to be met with in great abundance after 

 death. In living and healthy persons, from one to three or four of 

 these entozoa are contained in each follicle. They are more nume- 

 rous in the follicles situated in the depression by the side of the 

 nose ; but they are also found in those of the breast and abdomen, 

 and on the back and loins. Their form changes in the progress of 

 their growth. The perfect animal presents an elongated body, di- 

 visible into a head, thorax, and abdomen. From the front of the head 

 proceed two moveable arms, apparently formed for prehension : and 

 to the under side of the thorax are attached four pairs of legs, termi- 

 nated by claws. The author distinguishes two principal varieties of 

 the adult animal ; the one remarkable for the great length of the 

 abdomen and roundness of the caudal extremity ; whilst the other is 

 characterized by greater compactness of form, a shorter abdomen, 

 and more pointed tail. The first variety was found to measure, in 

 length, from the one-lOOth to the 45th, and the second, from the 

 one-160th to the 109th part of an inch. 



The author gives a minute description of the ova of these entozoa, 

 which he follows in the successive stages of their developement. 

 The paper is accompanied by numerous drawings of the objects de- 

 scribed. 



2. " On Factorial Expressions, and the Summation of Algebraic 

 Series." By W. Tate, Esq. Communicated by the Rev. Henry 

 Moseley, M.A., F.R.S., &c. 



This paper, which is wholly analytical, contains an investigation of 

 certain general methods for the summation of algebraic series, which 

 have led the author to the discovery of some curious and elegant pro- 

 positions relative to factorials and the decomposition of fractions ; 

 and also to a new demonstration of Taylor's theorem. 



3. " Notice of the Comet ;" in a Letter from Captain John Grover, 

 F.R.S., addressed to P. M. Roget, M.D., Sec. R.S., and dated from 

 Pisa, March 21st, 1843. 



The author states that at Pisa, on Friday, the 17th of March, 1843, 

 at eight o'clock in the evening, he saw a luminous arc in the heavens, 

 extending from a spot about a degree to the south of Rigel to some 

 clouds which bounded the western horizon. It was about 40 minutes 



Phil. Mag, S. 3. Vol. 23. No. 153. Nov. 1843. 2 B 



