LEROY C. COOLEY. 127 



these illuminations the opaque divisions of both scales 

 may be distinctly projected. 



The grooved standard and the rubber tube are features 

 borrowed from a German apparatus figured in Wein- 

 hold? s Physics. 



The following are believed to be novel : 



First, The substitution of a counterpoise for clamps 

 in lifting and lowering the mercury-tube. 



Second, The placing of the zeros of the scales at the 

 top and reading downward. 



Third, The use of an adjustable scale to measure the 

 heights of the mercury column ; and, 



Fourth, The use of a flexible and transparent scale. 



FEBRUARY 13, 1884— TWENTY-FIRST STATED MEETING. 



Prof. W. B. Dwight, chairman, presiding ; fifteen 

 members and guests present. 

 Prof. W. B. Dwight gave a description of the 



EMBRYONIC FORMS OF LimullLS polypJiemUS— RING CRAB. 



Specimens of the larvae of the "king crab" L. polyplie- 

 mus were shown in the stage of development immediately 

 subsequent to their hatching from the egg, which were 

 four millimeters in length. At this stage the abdominal 

 spine is either entirely unformed, or, more generally, 

 barely indicated in its rudimentary condition. Although 

 these larvge must be in abundance on our shores, for some 

 reason they were rarely seen or collected by scientists. 

 These were discovered in a crowded mass or nest in the 

 sand, on the shore of a lagoon, at Martha's Vineyard, 

 Mass. They were the first he had found on the seashore, 

 and on inquiry, he had ascertained that there were no 

 specimens of them in many of our leading museums. 



The larval forms of the Limulus bore important rela- 

 tions to the extinct trilobite, the facts pertaining to 

 which were first discovered by Prof. Samuel Lockwood, 



