88 



CRUSTACEANS 



young crayfish is unlike the adult in form, and approaches 

 maturity only after passing through many changes 

 (Figure 84). 



79. Molting. — One of the interesting features in the 

 study of the crayfish is the shedding of the external skele- 

 ton. Being covered by a firm exoskeleton it is necessary 

 that this be removed occasionally, in order that the animal 

 may grow. Molting, in the case of the crayfish, is a 

 serious and dangerous operation, as it is followed by a 

 period during which the crayfish is without means of 

 offense or defense. The crayfish usually hides until a new 

 exoskeleton is partially formed. In the molting process 

 the covering of the eyes and part of the lining of the diges- 

 tive tract, as well as the whole exoskeleton, are shed. 

 The crayfish molts every year of its life and several times 

 during the first year (Figure 85). 



LABORATORY STUDY 



Place several crayfish in jars or aquaria and observe their behavior. 

 Fill out the following report : 



DO THEY 



Move the 

 Antenn.e? 



DO THEY 



Walk 

 Forward ? 



Do THEY 



Walk 



Backward ? 



Do they Use 

 Caudal Fin ? 



Do THEY 



Move Eyes ? 



What Organs 

 Make a Cub- 

 rent in 

 Water ? 



Laboratory study on the appendages. Examine more fully than in 

 the above and report the work of each pair of appendages. Compare one 

 of the abdominal appendages with those used in walking and feeling. What 

 is the work of the large pinchers ? How many fin-like appendages are 

 found in the mouth region ? Notice that one of the mouth appendages 

 has a flat part that extends in front of the gills. This part of the append- 

 age is called the gill scoop or bailer. 



