ZOOLOGICAL SOCIETY BULLETIN. 



927 



any species ma}^ extend over a considerable 

 period — in Camharus bartoni, for example, from 

 March loth to May loth. Chidester* has ob- 

 served that in C. bartoni var. bartoni there is 

 also an autumnal sjjawning season beginning 

 with the latter part of September and extending 

 through October and November. Although Chi- 

 dester does not discuss the matter, this probably 

 does not mean that two broods are produced in 

 a season, but that some of the females mature 

 their eggs in the spring and others in the fall. 



Andrews! has carefully studied the reproduc- 

 tion of Cambarus affinis. Three hundred to six 

 hundred eggs, of a diameter of about one and 

 one-half millimeters, are produced. These, as 

 in the lobster, become attached to the under side 

 of the abdomen, especially on the swimmerets, 

 by adhesive portions of the egg envelopes. The 

 eggs are laid in April and ^lay and hatch in a 

 few weeks, the time apparently depending on 

 the temperature of the water. 



When first hatched each young craj'fish is at- 

 tached by the telson thread, a string of cuticle 

 fastened at one end to the telson or last ab- 

 dominal segment and at the other to the now 

 empty egg membrane. In this condition they 

 remain for two days, when they moult and pass 

 from the first stage to the second. In the 

 second stage also the }-oung are inactive and re- 

 main with the mother, but the telson thread is 

 lost and they remain attached by grasping the 

 old egg cases and the abdominal setae with their 

 pincers. During this time they eat nothing and 

 the yolk sac is gradually absorbed. After six 

 days in this condition the skin is again moulted 

 and the V'oung emerge in the third stage. By 

 this time they have taken on the form of the 

 adult, except that the proportions are somewhat 

 different. 



The third stage marks the beginning of active 

 life, and, while the 3'oung remain with the 

 parent more or less closely for a week or so, thej- 

 gradually wander away and begin an independ- 

 ent existence. By fall the young ordinarily 

 reach a length of about two inches and are sexu- 

 ally mature, and the first pairing takes place in 

 October or November of the first year. 



After this there are no more moults and con- 

 sequently no growth until the young have been 

 produced in the following spring. 



How long crayfishes live has been ascertained 

 for only a few species. Andrews found no 

 specimens of Cambarus limosus living after the 

 third summer, and Ortmann states that, except 

 in occasional individuals, three years constitutes 



tiie life period of C. obscurus. The European 

 crayfish Astacus fluviatilis, has been known to 

 live six years. 



Size is dependent largely upon the species. 

 Some of our smaller species do not attain a 

 greater length than a couple of inches. C. 

 limosus reaches a maximum of about four 

 inches, while the European Astacus fluviatilis 

 grows to nearly eight inches. The largest 

 species known is Astacojisis franklinii, found in 

 small streams of Tasmania, which reaches a 

 weight of eight or nine pounds and is thus about 

 equal in size to the European lobster. 



The crayfish has many natural enemies. Per- 

 haps the most destructive are various species of 

 fishes, the larger salamanders, such as the mud- 

 puppy {Necturus) and hellbender {Crypto- 

 branclnis) and water-snakes. No doubt the 

 semi-aquatic mammals take their toll and the 

 raccoon is said to be particularly fond of them, 

 ^lany aquatic birds feed upon them. They are 

 parasitized by leeches, copepod crustaceans and 

 worms. The shells are often overgrown with 

 diatoms and algae, and those from our park 

 lakes are often covered with a profuse growth 

 of a large colonial protozoan {Epistylus). It 

 is doubtful if these do any particular harm, ex- 

 cept, perhaps, to impede the progress of the 

 crayfish when the growth is abundant. Fur- 

 thermore, all craj-fishes are given to cannibalism 

 to some extent, and not only are young devoured 

 by the adults, but full-grown specimens, when 

 shedding, may be attacked and devoured before 

 the new shell has had time to harden enough to 

 serve for a protection. 



'American Naturalist, May, 1912. 

 fSmithsonian Contributions to Knowledge, vol. 

 XXXV, 1907. 



CRAYFISH COVERED WITH PROTOZOANS 

 OiK'-liiilf natuml size, rliutosr.ipli by K. C. Osburil. 



