OF THE SHELL OF CRUSTACEA. 89 



degrees of development and position of tlie laminae and tubules. In 

 the group Anomura, or soft-tailed crabs, and of which the soldier 

 and hermit crabs are members, the difference of structure is not 

 very great, and this agrees well with the known difficulty that is 

 often found in separating some of the members of the two 

 groups. 



In the group Macroura, represented by the lobster, shrimp, cray- 

 fish, &c., the difference is considerable, although not so great as 

 one would conclude from a more casual inspection. The calcareous 

 matter in the corium of the lobster is very dense and opaque, 

 rendering it difficult to make a good transparent section, whilst in 

 the common shrimp a section of the shell at right angles to the 

 surface shows the four layers present, but in a very attenuated form, 

 and the calcareous matter locally diffused. 



The most remarkable feature in the integument of the shrimp 

 consists of numerous discs, the result of a secondary calcification, 

 which becomes incorporated with the pre-existing tubulated calcific 

 deposit. The brovra carapace of Argulus foliaceus, mounted in 

 dilute glycerine, shows well the hexagonal divisions of the areolar 

 layer. 



In examining a portion of a cast shell of Liinulus, a junior speci- 

 mien, I foimd very little calcareous matter. Throughout the pre- 

 paration were to be seen a number of centres which, under the 

 polariscope, showed the black cross, beautifully defined, and closely 

 resembhng those centres shown in an elytron of a coleopterous 

 insect. 



At the close of the paper, 



Mr. Martinelli called attention to the fact that the cuticular 

 layer becomes separated if the shell be treated with dilute hydro- 

 chloric acid. 



Mr. Breese stated that he had utterly failed to make out the 

 tubes in sections prepared in the usual way. In pieces chipped 

 across the shell at right angles to their directions he had, however, 

 detected them with the one-eighth objective. He believed that the 

 grinding process filled up the tubes, and thus rendered them in- 

 visible. He had tried hydro-chloric acid, but had failed to separate 

 the layers so as to render the tubes visible. 



H 2 



