738 Comparative Animal Physiology 



hepatopancreas of inorganic constituents for a new exoskeleton; (2) molt, 

 the splitting and shedding of the old, partially resorbed cuticle, and an 

 abrupt size increase largely due to absorption of water; (3) postmolt, a pe- 

 riod of rapid redeposition of chitin and inorganic salts to produce a new 

 cuticle, and of protoplasmic growth; and (4) intermolt, a period during 

 which physiological processes normally associated with the molting process 

 are largely held in abeyance. In the fresh-water crayfish, Camharus, on which 

 most of our knowledge of hormonal integration of the molting phenomenon 

 is based, there is no true larval stage; the individual hatches as a diminutive 

 adult. During its first year of life it molts at intervals of about 12 to 13 days, 

 probably without intervention of any significant intermolt period. After the 

 first growth season there are usually two molts a year, one occurring in the 

 spring, in late April or May, and the other in the summer, in July or Au- 

 gust. In these older, mature crayfishes the premolt period is 3 to 5 weeks. 

 During this time there is a gradual resorption of the exoskeleton and 

 a deposition of calcium salts in the form of gastroliths in the antero-lateral 

 walls of the cardiac stomach. There is also a gradual increase in the rate of 

 oxygen consumption and of water content for a week or so prior to molt, 

 reaching a peak at the time of molt. The period of postmolt is one in which 

 these changes proceed in the opposite direction and require approximately 

 the same time as the corresponding processes of premolt. Postmolt is fol- 

 lowed by intermolt, which is of longer duration after the summer than after 

 the spring postmolt. 



Observations on changes associated with the molting cycle in other crusta- 

 ceans show that the hepatopancreas is a site of storage of calcium salts in 

 certain of the crabs. The stored salts are not sufficient to account for the nor- 

 mal hardening of the exoskeleton, thus making it necessary that the postmolt 

 period is one of rapid absorption of calcium, both directly from the external 

 medium and from ingested food. A study of apparent respiratory quotients 

 of crayfishes shows that although animals in intermolt have a quotient of 

 about 0.8, freshly molted crayfishes show values as low as 0.1-0.2 during 

 the first few postmolt hours because of CO2 fixation during carapace harden- 

 ing, and that this value gradually increases to 0.7-0.8 during the first post- 

 molt week. This obviously indicates that calcium is very avidly taken up from 

 the surrounding medium immediately after molt, and that the rate declines 

 rapidly during the first few days. 



It is known that removal of .the eyestalks from Astacus,^^'^ Uca,^- ^^ Erioch- 

 eir,''^ Palaemonetes,^^ or Camharus^^' ^^^ results in a more rapid onset of the 

 following and succeeding molts. In young Camharus, in their first year of 

 life, removal of the eyestalks results in a shortening of the period between 

 molts at 20 to 22° C. from about 12 days to about 8 days.^"*^ That this in- 

 fluence is not the result of general operative injury is seen in that other 

 operative injuries, such as destruction of the retinas, which are at least as 

 severe, do not result in such acceleration; if any influence is seen there is a 

 retardation. The remaining two possibilities, that the results are due to (1) 

 the destruction of important nerve centers, or (2) the removal of endocrine 

 organs important in molt regulation, have been resolved in favor of the 

 latter. If both eyestalks are removed from mature crayfishes molt will occur a 

 significant time in advance of that of unoperated controls. If, however, sinus 



