9^6 



ZOOLOGICAL SOCIETY BULLETIN. 



CRAYFISH 



In the water the crayfish balances himself easily on the 



walking legs Photograph by II. ('. Osburn 



with pale bluish on the upper part of the thorax 

 and abdomen and on the legs. There is no indi- 

 cation anywhere of the dark green or blackish 

 pigment, and the onby red to be observed is a 

 faint tinge of this color in the region where the 

 abdominal spots occur in the normal form. No 

 structural differences have been observed. 



Cases of partial albinism or suppressed de- 

 velopment of color have been noted occasionally 

 in various species of animals. Of the crayfish 

 Dr. Ortmann writes thus in reply to a recent let- 

 ter: "The pale blue color-variety is very re- 

 markable indeed. Bluish specimens, as a color- 

 variety, have been described in European spe- 

 cies of Potamobius (Astacus), but have always 

 been regarded as extraordinary cases. I have 

 occasionally observed slate-blue specimens in 

 Cambarus bartoni, but always single individuals 

 only. I have received specimens of a whitish 

 variety of C. virilis from Sandy Lake, Peter- 

 boro County, Ontario, Canada, a lake remark- 

 able for its limestone deposits, but here they 

 are all said to be of this color." 



More than two dozen specimens of this pale 

 phase of C. limosus, of both sexes, have been 

 taken at different times in Prospect Park Lake, 

 Brooklyn, during the past two summers, among 

 about two hundred of the ordinary color phase — 

 no exact counts were made. 



What may be the cause of the suppression of 

 the ordinary colors in this and similar cases 

 of partial albinism is not known. Whether it is 

 due to some congenital variation (mutation or 

 saltation), which would then be hereditary, or 



whether it is due to some physiological condi- 

 tion developed during the life of the individual 

 is unknown, and could only be determined by 

 breeding experiments. From the number of 

 specimens and from the fact that they were 

 taken living with the ordinary variety, it seems 

 probable that the difference is congenital and 

 due to the suppression of a color-developing fac- 

 tor. This assumption is further borne out by 

 the fact that color is not entirely absent, but 

 merely suppressed in large part. 



The reproduction of the crayfish is very in- 

 teresting and has been the subject of much 

 study in this county, especially by Professor 

 E. A. Andrews,* of Johns Hopkins University. 



It has long been known that the crayfishes 

 have no larval surface-swimming stages as do 

 their marine relatives, the lobsters and prawns. 

 As early as 1755 von Rosenhof noticed that the 

 young of the European crayfish are similar to 

 the mother and that they remain with her for 

 a time after hatching. Rathke in 1829 showed 

 that the young emerges from the egg in essen- 

 tially the adult form and so has no metamor- 

 phosis. Later, however, Huxley (1879) proved 

 that the young before the first moult are not ex- 

 actly similar to the adult, but differ in the lack 

 of setae, or bristles, and in the form of the 

 first and sixth abdominal appendages. Thus 

 it will be seen that there is only a slight degree 

 of metamorphosis and of a different sort from 

 that seen in the marine Crustacea. 



The reason for the elimination of the free- 

 swimming stages is probably to be found in their 

 adaptation to a special habitat. If a surface- 

 swimming stage were present, as in the lobster, 



A FEMALE CRAYFISH 



Showing method of carrying the eggs. 

 Photograph by R. C, Osburn. 



the young of the mountain stream species might 

 lie carried into the larger streams, while those 

 of the inhabitants of the lowland streams might 

 even be carried out to sea at this period. 



The eggs of the crayfishes are regularry laid 

 in the early spring and the time of laying for 



*The Young of the Crayfish, Astacus and Cam- 

 barus. Smithsonian Contributions to Knowledge, vol. 

 XXX. pp. 1-79, plates I-X. 



