THE NEWLY-HATCHED CRAYFISH. 219 
The posterior cephalic and the thoracic appendages 
(5—14) elongate and gradually approach the form which 
they possess in the adult. I have not been able to 
discover, at any period of development, an outer division 
or exopodite in any of the five posterior thoracic limbs. 
And this is a very remarkable circumstance, inasmuch 
as such an exopodite exists in the closely allied lobster 
in the larval state; and, in many of the shrimp and 
prawn-like allies of the crayfish, a complete or rudi- 
mentary exopodite is found in these limbs, even in the 
adult condition. 
When the crayfish is hatched (fig. 60) it differs from the 
adult in many ways—not only is the cephalothorax more 
convex and larger in proportion to the abdomen; but the 
rostrum is short and bent down between the eyes. The 
sterna of the thorax are wider relatively, and hence there 
is a greater interval between the bases of the legs. than in 
the adult. The proportion of the limbs to one another 
and to the body are nearly the same as in the adult, but 
the chele of the forceps are more slender. The tips of 
the chele are all strongly incurved (fig. 8, B, p. 41), and the 
dactylopodites of the two posterior thoracic limbs are hook- 
like. The appendages of the first abdominal somite are un- 
developed, and those of the last are inclosed within the 
telson, which is, as has already been said, of a broad oval 
form, usually notched in the middle of its hinder margin, 
and devoid of any indication of transverse division. Its 
margins are produced into a single series of short conical 
