HOMARUS AMERICANUS MILNE-EDWARDS 139 



mal skeleton and the stomach. Put the latter aside for future 

 study. Wash the skeleton in water. Place it in its natural 

 position, sternites down, anterior end away from you, and make 

 a natural-size drawing showing the entire endophragmal skeleton 

 viewed from above. It will be noticed that it consists of a mesh- 

 work of thin lamellae or apodemes of which there are two pairs 

 between every pair of adjoining segments. In the position 

 indicated there are visible three rows of meshes. The internodes 

 of the median row are formed each by two horizontal plates 

 or mesophragmata constituting a part of the endosternites. 

 The walls of each mesh of the median row are formed mainly 

 by the endopleurites and partly by the paraphragmata or lateral 

 plates of the endosternites. Each paraphragma articulates 

 with an endopleurite. In the depth below the mesophragmata 

 the sternites of the exoskeleton are visible. The sternites 

 form the floor, the mesophragmata the roof of the sternal canal. 



6. Carefully isolate one of these endophragmal segments 

 which have openings for pleurobranchiae by cutting its con- 

 nections with the adjoining segments. Make a natural size 

 drawing of it looking into the sternal canal. The sides of the 

 sternal canal are formed by the endosternites, the roof by the 

 mesophragmata of the endosternites, the floor by the sternite 

 of the exoskeleton. The endopleurites will be seen to the outside 

 of the endosternites. Each endopleura has a hard articulation 

 point for the coxopodite of the corresponding appendage. 



7. Make a drawing, three-fourths view, of the abdominal 

 segment showing tergite, pleurae, sternite, epimeron and sockets 

 of pleopods. On the tergite show the portion covered by the 

 preceding segment and clearly separated from the rest by a 

 groove. 



8. Make a drawing l of the first antenna showing the three- 

 jointed protopodite; the membrane covering the otocyst and the 

 pore leading into the otocyst on the first joint of the protopodite; 



1 Drawings 8 to 1 6 to represent the ventral aspect of the appendages, i. e., 

 showing the surface normally visible in a lobster turned on its back. 



