300 



THE CRUSTACEA 



the uropods are the last to appear. In Nepliwps (Fig. 177) the 

 course of development is very similar, liut the larvae are 

 distinguished by the long spines of the abdominal somites and 



telson. The freshwater Cray- 

 fishes have a direct develop- 

 ment, the young on hatching 

 resembling the adult in most 

 points, but lacking the first 

 and the last pairs of abdominal 

 ajipendages. 



The Scyllaridea have a 

 very peculiar and character- 

 istic series of larval forms, 

 which were long described as 

 adults under the generic name 

 Phi/Uosoma (Fig. 178). These 

 PiQ. 176. larvae are remarkable for the 



Larva of American Lobster {Homirus ameri- large size tO which SOme attain, 



cana.->), in Sehizopod-stage. a', antennule ; n", i p i • in 



antenna ; mf", third maxilliped ; pi-pr, the five and lOr their extremely Iiat- 



pairs of lej^s. (After 8. 1. Smitli, from Kor- , i ji tti r^„ i 



^che\t and Heuier-s Embrjioiog,,.) teued and leaf -like form and 



glassy transparency. The body 

 is sharply divided into three regions. The first, Avhich is covered 

 by the oval carapace, includes the head and the first two thoracic 

 somites. The remainder of the thorax forms a discoidal plate and 



Late Sehizopod-stage of Nephrops norveqious. «', antennule ; n", antenna ; mf", tliird 

 maxilliped ; jji-pS, the five pairs of legs ; pt^, pl^, pleoports ; r, rostrum. (After Sars, from 

 Korschelt and Heider's Emhryology.) 



is followed by the narrow and indistinctly segmented abdomen. 

 The last two thoracic appendages are not developed in the newly 

 hatched larva, but the four pairs in front of them are long and 

 slender, with natatory exopodites. The first thoracic limbs are 

 rudimentary (Palinurus) or absent {Sctjllarus), and the second pair 



