180 Rev. A. M. Norman on Recent Eryontidse. 



more than a passage or metamorphic form, would not be ex- 

 traordinary. But the great number of full-grown second-form 

 specimens in every species, which are often even larger than 

 the first-form males, seems to prove that they are individuals 

 which have remained in a sexual stage that does not agree 

 with their corporal development — in short, that they are per- 

 haps sterile. 



" The objection that these second-form males may be indi- 

 viduals shortly before or shortly after the casting of the skin, 

 I can surely refute, as I have seen many specimens at this 

 stage of growth, the museum collections exhibiting the ani- 

 mal in all the different phases of its existence. 



" Another objection, that the males of the second form, or 

 perhaps those of the first form, are abnormally developed 

 individuals, is refuted by the great number of the two forms 

 existing and living together. 



" The conjecture, on the other hand, that the second-form 

 males may be sterile, is really supported by the anatomical 

 examination of the two forms in the principal groups of Cam- 

 bar us" *. 



Not only so, but Hagen tells us of two forms of the other 

 sex, and that in certain abnormal females he finds " a ten- 

 dency to a more masculine development, as in the aforesaid 

 males a tendency to a feminine development "f. 



Mr. Bate informs us that he has females of six species of 

 Willemoesia and Pentacheles (that is, with chelate last perei- 

 pods) and males of two, and that he has males of three species 

 of Poly xheles with simple last pereiopods, and females of two. 

 As far as members go (but, of course, numbers are of little 

 or no value), this gives 9 to 4 in favour of my view. 



The exceptions are that he has males of Willemoesia lepto- 

 dactyla and Pentacheles Suhmi with chelate last feet. I have 

 hinted in this paper, from what we know to occur among 

 other Crustacea, that these males may be either immature, and, 

 not yet having attained their full sexual characters, exhibit 

 still the female form of the limb, or that they may be in- 

 stances of dimorphous (sterile) males. Indeed it would 

 seem that Mr. Spence Bate is not without doubts as to the 

 location of some of the forms he has described as species ; 

 for immediately after the list he adds, " For some time I was 

 hesitating where several species of Pentacheles should be placed, 

 as there is a regular gradation from the imperfect to the perfect 

 chelate character of the fifth pereipod ; but as I found Poly- 

 cheles, both male and female, with the simple non-chelate foot, 



* Hagen, ' Monograph North- American AstacicUe,' 1870, p. 22. 

 t Hagen, /. c. p. 17. 



