22 G. C. Embody. 



The movements continued with diminishing intensity and at 12 M., 

 the amphipod was dead without having crawled from the old skin. 



Four other similar cases came under observation. A fifth specimen 

 (G. limnaeus), moulted in two hours completely shedding the old skin 

 but was found dead ten minutes later. 



It was very evident that the moulting of the female at least, if for 

 any reason prolonged might bring about such a weakened condition as 

 would result in death. Such a weakened female even if possessed of 

 sufficient vitality to live through the process, might fall an easy victim 

 to a vicious and hungry male. 



EX. Growth of yoimg. 



Broods of young representing the four speciers here treated and 

 whose hatching dates were known, were isolated in different aquaria 

 each of about a gallon capacity. Bottom sediment including a few 

 dead leaves was supplied to each aquarium together with living plants 

 of Elodea, Chara and Ricciocarpus. It was customary to take 

 three individuals of each species at different ages and kill them in 95 per- 

 cent alcohol containing 7 percent formaldehyde.^) They were then care- 

 fully straightened out and with a short steel measure graduated in 

 hundreds of an inch, the length of each individual exclusive of the 

 antennae was taken by the aid of a disecting microscope. The results, 

 while not complete, cover a long enough period to show considerable 

 diversity in the rate of growth of certain species and to throw some 

 light upon the question concerning the age at which each form reaches 

 sexual maturity. 



AU recorded measurements reduced to milhmeters together with the 

 ages in days are tabulated as follows on p. 23. 



The four curves on page 24 have been plotted by using the data 

 (lengths and ages) in table XI as coordinates. 



Of the four species it can be seen that G. limnaeus and G. 

 fasciatus, grow most rapidly, Hyalella ranking third and E. gra- 

 cilis last. 



The young amphipods which furnished the data in Table XI were 

 watched closely with the hope that some might exhibit signs of sexual 

 activity. — The Hyalellas alone rewarded the effort. At the age of 

 forty-three days two pairs of young were mated and on the forty-fifth 



*) With these proportions it was found that the fixed amphipods retained the 

 size and form of the living ones. 



