12 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 21 



Growth and Sexual Maturity 



Dr. Pierre Drach of the Faculty of Science, University of Paris, in 

 a recent communication stated that the common European species of 

 Majidae achieve sexual maturity only following the last molt, which he 

 terms the puberty molt. It is at this time that the male chelipeds sud- 

 denly increase in size and the female abdomen broadens to encompass 

 most of the sternum, becoming convex externally. While it cannot be 

 stated unequivocally that this is true of the common North American 

 species, for lack of life history studies, its extension to the fauna under 

 consideration as a working theory or hypothesis is most helpful in ex- 

 plaining some of the phenomena noted in the section on Growth and 

 Development in the pages that follow. Among the Acanthonychinae, for 

 example, males of Taliepus nuttalli (Randall) in the 37-61 mm length 

 range show no cheliped enlargement, while in a 106 mm male the 

 chelipeds are grossly enlarged. The single ovigerous female, 83 mm long, 

 is evidence that the smaller males are pre-puberal, and that sexually ma- 

 ture males must lie in the 83-106 mm range. Again, in the Ophthalmiinae, 

 the discrepancy between the short cheliped found to be characteristic of 

 our males of Pitho picteti (Saussure), the type of which was described 

 as long-armed, and the customarily long cheliped of P. quinquedentata 

 Bell, might be due only to the absence of a post-puberal male from our 

 series of the former species. 



Dr. Drach also pointed out that changes in the male first pleopod 

 may occur at puberty, including a sudden lengthening of the appendage 

 and its reinforced sclerotization. It should be borne in mind in this con- 

 nection that while an attempt was made to figure pleopods from mature 

 specimens only, in numerous cases such specimens were not available, 

 necessitating the figuring of immature males. Where after figuring the 

 pleopod of an immature male, a mature male has become available, as in 

 the case of Taliepus marginatus (Bell) from among Lund University 

 Chile Expedition collections, discrepancies have been observed that are 

 best explained on this pre- and post-puberal basis. This does not mean 

 that the pleopod is any the less useful as a taxonomic character because 

 of changes that may take place with growth, but rather that in a number 

 of species pre- and post-puberal forms of the male pleopod may have to 

 be taken into account. The extent and nature of such change will become 

 apparent from studies made in the Oregoniinae, of which pleopods of 

 males from two year-classes of Chionoecetes bairdi Rathbun (Plate I, 

 figs. 6 and 9) are illustrated. From this comparison it will be seen that 



