The progression of the morphological features of the male blue crab reproductive system that culminate in puberty involves one change in the gonad, four combinations of the method and degree of adherence of the abdomen to the sternum, four variations in the positions of the penes, and four variations in the positions of the pleopods. The sequence of development appears to be established: (I) spennatophores must be present in the anterior vasa deferentia; (2) the abdomen must be completely free of the sternum, or, in addition, may be locked by the sternal tubercles; (3) and the penes and second pleopods must be inserted in the first pair of pleopods
