238 PEOGEESS OF MICEOSCOPICAL SCIENCE. 



places two flames, such as night-lights, at known distances apart, and 

 using the objective alone without any tuho, has a very convenient 

 scale of tangents engraved upon paper, thus showing the angle by 

 inspection. This is described in the ' Mouth. Mic. Journ.,' July, 

 1875, p. 3. In the 'Month. Mic. Journ.' for May, 1874, p. 178, 

 Mr. Wenham describes an adjustable slit formed by two slips of very 

 thin platina foil, which can be separated to the exact diameter of any 

 field of view, thus excluding all but " image-forming rays." This is 

 a very valuable adjunct, and greatly conduces to accuracy ; and when 

 used with a divided circle, with small flames at a suitable distance, or 

 white crosses on a black ground, and with a lens or lenses centered 

 and sliding above the eye-piece, it forms a very suitable and accurate 

 combination. 



The Development of Gasieropod Mollusks. — We learn from a note in 

 the ' American Naturalist ' for March, that at a meeting of the Boston 

 Society of Natural History on February 2, Dr. W. K. Brooks read a 

 paper on the development of Astyris (Columbella) lunata. This, that 

 jom-nal states, is the first siphonated gasterojwd whose embryological 

 history has been followed. Some general views on the moUuscan 

 pedigree were added. 



State of Chord in Death from Paresis. — Dr. C. E. Mann says * that 

 in a recent case of death which occurred in a person who suffered from 

 Paresis, upon hardening the spinal chord and making thin sections, and 

 employing carminal staining to demonstrate the structural relation 

 more clearly, there were found to be, upon microscopical examination, 

 atrophy and degeneration of the nerve elements of the posterior 

 columns, with increase of connective tissue. Sections of hardened 

 brain-tissue being made, there was observable, in the cerebral cells of 

 the frontal convolutions, a diffused granular degeneration. No change 

 could be detected in the cerv'cal sympathetic, which was carefully 

 examined. 



Difficulties of Classification of the Spongida. — Mr. H. J. Carter, who 

 has recently written ujion this subject, says, in a report published in 

 the ' Annals of Nat, Hist.,' that in the general classifieation of the 

 Spongida there is not much difficulty, as the skeleton (which too often 

 is the only part that reaches us, from the inaccessible places in which 

 many of them grow and the accidental circumstances under which 

 they reach the shore) consists of durable material which, in structure 

 and composition, admits of very easy arrangement ; while where there 

 is no skeleton at all, this alone for such sponges is sufficiently 

 characteristic of the order. But in the more particular classification 

 there are peculiar difficulties, inasmuch as there is no expression in 

 sponges as in other animals and in plants ; that is, there is nothing 

 like a calice, as in the coral, and nothing like a Jloiver, as in the jjlant, 

 to guide us — what there is in this respect, viz. the spongozoon, being 

 microscopic in size, undistinguishably alike and so protean in form as 

 only in its active living state in situ, or just after it has been elirainatad 



* ' New York Med. Journal,' Febriiary. 



