High and low Dimorphisin. 319 



quently met with measuring about 4 mm. This latter larvai form 

 never metamorplioses into the adult, but probably attaches itself 

 again to a fish aud does not become adult until after passing again 

 into the Prauiza state. Although ali the points contended for in my 

 paper were by uo means satisfactorily proved, the following faets 

 are certain. 



1. The adult male does not go on growing after attaiuing ma- 

 turity. 



2. Its range of size is immense, varying in the males from 

 1 — 8 mm. : this range of size being dependant on the amount of time 

 spent in the larvai life. 



3. A large sample of males eollected during full breeding-time 

 feil into a distinctly bimodal curve in relation to size. 



4. Correspondìng to the two modal sizes, the males feil into two 

 groups which showed somewhat different frequencies with respect 

 to the measurement of an index describing the shape of the man- 

 dible, but owing to the difficulties of measurement I cannot lay much 

 stress on this point. 



5. At certain points in the larvai history, but espeeially at the 

 period of medium growth, i. e about 4 mm., a special retrogressive 

 larva occurred which never passes to the mature condition from 

 that state. 



These facts appear to me sufficient to show that in this species 

 in the Bay of Naples there is an antagonism between growth and 

 maturity which tends to establish a division into high and low 

 males. 



B. Leptochelia dubia. (The reasons for assigning the limitations 

 to this species are given in Appendix 1 , pag. 333 — 335 , and also 

 the relation of the males I have found to those of Feitz Müller). 



The males are distinguished from the females of this species 

 by the greater size and different structure of the chela and of the 

 first antennae. Males are fìgured in Piate 20, Figs. 1 — 2 and fema- 

 les in Figs. U — 13. The males up to the last ecdysis but one resemble 

 the females; in the last ecdysis but one they assume the form 

 showu in Fig. 10, and from this form they pass to the full adult 

 condition which is permanent, the male ceasing to grow after this 

 point. 



The males differ greatly in size, from 2-^4 mm. in length, and 

 with this difference in size is associated a marked dimorphism, the 

 larger males having immensely developed ehelae (Fig. 7) while the 



