EXTRACTS AND ABSTRACTS FROM FOREIGN JOURNALS. 89 



dia, of an olive colour, are oblong, above g^th of a millimetre, slightly 

 curved, and provided with from 3 to 5 partitions, obtuse at their extre- 

 mities, where a filiform, transparent, short and sharp appendage may be 

 seen. The theca of Sphceria caulium, on the contrary, is longer and 

 very apparent ; its sporidia, of a pale greenish colour, measure aVth of 

 a millimetre ; they are slightly curved, provided with from 5 to 7 

 partitions, and pointed at the extremities, to which no appendage is 

 attached. March, p. 145. 



Explanation of the Figures. 



PLATE III. Div. 3. a, Thecsa and sporidia of Sphceria caulium magnified 500 times. 

 b, Thecae and sporidia of S. insidiosa, magnified likewise 500 times. 



Montagne on the use of the Compressor in the examination of Lichens. 

 As an essential desideratum to a good achromatic microscope, I will 

 mention the instrument called Compressorium, brought to perfection by 

 M. Schiek of Berlin. I cannot too strongly recommend its employ- 

 ment to those who are occupied with researches on the structure of cer- 

 tain parts of Cryptogamic plants, and in particular, the thecae of Lichens. 

 It would be almost impossible, without its assistance, to verify the facts 

 I have recorded. March, p. 147. 



Dufour on Anatomical and Physiological studies of a species of Musca, 

 with the view of illustrating the History of Metamorphoses, and the Pre- 

 tended Circulation of Insects. This paper is one of some length ; but the 

 author, from his dissections, experiments, and reasonings, concludes, 

 that the existence of an aeriferous vascular system adapted to convey the 

 physiological benefits of respiration to all the organs and tissues, is in- 

 compatible with the presence of a circulating humour. He is satisfied 

 that the latter does not exist in insects provided with tracheae, and that 

 the organ which has been supposed to perform this function, is merely 

 rudimentary, bearing some resemblance to the heart of the Arachnides ; 

 in fact, an obsolete heart, an organ deprived of every well- determined 

 physiological attribute, and perhaps a mere elementary tissue. July, 

 1841,^.5. 



[From the Comptes Rendus, 1841.] 



Biot on Achromatic Lenses with multiple Glasses in the Eye-piece. This 

 communication, which is here only given in abstract, relates especially 

 to Telescopes, and is only quoted in this place, as a reference for opti- 

 cians, and those interested in instruments used for astronomical pur- 

 poses. 6th Dec. 1841, p. 1039. 



Joly on Isaura cyclado'ides. The author at the termination of his 

 Memoir arrives at the following results: 1, The Isaura cyclado'ides 

 constitutes a new genus of the Crustacea Branchiopoda, near to Apus, 

 Limnadus, and Cyzicus of M. Audouin ; 2, In form, structure, and mode 



