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backwards — an action which would not require the cooperation 

 of the lower jaw. So we may believe, that while the upper jaw 

 has a power much greater than that of other carnivorous ani- 

 mals, the lower jaw has actually less. 



A second peculiarity of the lower jaw is the great depth of 

 the chin, which has given rise to the name Megantereon, in 

 which character it is more remarkable than any other animal of 

 the Cat kind. The long, contracted space between the lower 

 canine and first premolar seems destined to give room for the 

 movement of the point of the large upper canine. 



The teeth of the lower jaw correspond generally with those 

 of the other members of the family. There are three incisors, 

 one small cuspidatus or canine, two premolars, and one molar 

 on each side. 



Prof. Wyman called the attention of the Society to 

 several points in the specimen presented which attracted 

 his observation. The zygomatic arches were remarkable 

 for their great narrowness, not being laterally wider than 

 those of the Tiger, while the vertical width was much 

 greater, for the attachment of the masseter muscles ; for 

 the insertion of which there was also a marked depression 

 in the lower jaw. 



Dr. Burnett read a paper on the development of the 

 Spermatic Particles in decapod Crustacea, and exhibited 

 several diagrams, representing their singular forms. His 

 observations were made on the common Lobster, (^Astacus 

 marinus,) Pilumnus, Grapsus, and several other genera. 

 He had found that the particles in question are produced 

 from the nuclei of cells inclosed within a parent cell. 

 This nucleus is at first spherical, then oblong, and subse- 

 quently three tail-like processes spring from one end. 

 Thus these Spermatozoa are found to follow the same 

 general law of development as those of other animals, and 

 do not furnish exceptions to the general rule, as supposed 

 by Kolliker and Wagner, who regard the processes as the 

 true Spermatozoa. This latter opinion Dr. Burnett ascribed 

 to the fact, that when immersed in fresh water the ray-like 



