108 



SCIENCE 



[N. S. Vol. XXXIX. No. 994 



types of tissue cells will appear in later papers. 

 Similar experiments were tried with the tissues 

 of crayfishes and crabs with little result beyond 

 keeping these cells alive for several weeks. 

 The blood corpuscles of the crayfish were kept 

 alive and active for three months. 



S. J. Holmes 



NOTE ON THE ABSORPTION OF CALCIUM DURING 



THE MOLTING OF THE BLUE CRAB, 



CALLINECTES SAPIDUS 



The problem of molting in crabs has thus 

 far been investigated, with one exception,^ 

 only from the morphological point of view.- 

 The following observations bear on certain 

 chemical phases of the process of hardening 

 following normal molting in the common blue 

 crab. 



The crab hardens by the deposition of CaCOj 

 within the tissues of the soft shell. Has this 

 Ca been absorbed and held in reserve during 

 the period of preparation for molting,^ or is it 

 absorbed from the sea-water during the actual 

 period of hardening? To test this matter, the 

 following procedure was employed. Three 

 pairs of crabs were chosen, each pair consist- 

 ing of a recently shed individual and of a 

 hard-shell individual of nearly the same size.* 

 A comparison of the Ca content of the indi- 

 viduals of the same pair should throw light 

 on the alternatives suggested. If the Ca con- 

 tent of the two members of each pair is equal, 

 then the Ca must be absorbed before molting 

 and held in reserve. If the Ca content of the 

 hard specimen is very much larger than that of 

 the soft, then the Ca must be absorbed after 



1 Irvine and Woodhead, Proc. Boy. Soe. Edinb., 

 Vol. 16, pp. 324-354, 1888-89. 



2 For a review of the literature on the natural 

 history of molting in Crustacea, see Herrick, Bull. 

 U. S. Bureau of Fisheries, Vol. XV., pp. 1-252, 

 1895. For this species of crab, see Hay, App. 

 Eep. U. S. Comm. Fish., pp. 395-413, 1904. 



3 Cf. Smith, Quart. Journ. Microsc. Sci., Vol. 59, 

 p. 272, 1913. 



* These were collected at the Beaufort, N. C, 

 station of the U. S. Bureau of Fisheries. The 

 writer is indebted to Dr. H. M. Smith, the com- 

 missioner, for the privilege of staying at the sta- 

 tion. 



molting. Furthermore, if the first alternative 

 is the true one, the Ca content of a crab in 

 the act of casting its shell should be much 

 greater than that of a normal hard crab. If^ 

 however, they have the same Ca content, then 

 the second alternative is indicated. 



Each crab was ashed separately, and the Ca 

 in the ash determined by precipitating it as 

 the oxalate, igniting and weighing as the 

 oxide. The results of the analyses are indi- 

 cated in the table. In each pair the hard- 

 shell specimen contains about twenty times 

 the amount of Ca contained in the soft one. 

 Also, Crab No. 9, which was in the act of 

 casting its shell, has a Ca content comparable 

 to that of a normal hard individual. 



This shows clearly that the Ca used by the 

 soft-shell crab for the purpose of hardening 

 its new shell is not present at the time of the 

 molt, but is absorbed from the sea-water dur- 

 ing the hardening. 



The mechanism by means of which a molt- 

 ing crab is enabled to absorb such abnormally 

 large quantities of Ca is at present obscure,, 

 and in view of the meager data at hand, a 

 discussion of this problem is best postponed 

 until more work shall have been done. 



Selio Heoht 

 Biological Laboratories, 



The College of the City op New York 



5 The width of the new shell was 9.8 cm. The 

 per cent, of Ca in this specimen is low because the 

 molting crab weighed more than an ordinary 8.5 

 cm. crab, and also because the old shell had two 

 legs missing, which were being regenerated. The 

 actual weight of Ca, however, is very close to that 

 of a normal hard crab. 



