PENAEIDAE. 



267 



B. Penaeidae. 



Our knowledge of the metamorphosis of Penaeus is due mainly 

 to the researches of F. Muller (Nos. 141 and 142). It is of great 

 significance in forming an estimate of the Decapodan metamorphosis, 

 on account of the presence of 

 the Nauplius stage, as well as 

 the primitive order retained in 

 the development of the seg- 

 ments and limbs. Claus (No. 

 8) has since added further de- 

 tails, especially with regard to 

 the Protozoaea stage. More 

 recent investigations have been 

 made by Brooks (No. 110), 

 who was able to observe the 

 origin of all the stages follow- 

 ing the first Protozoaea in 

 specimens cultivated by him. 

 A series of larval forms chiefly 

 belonging to later stages are 

 described by Spence Bate, who 

 utilised the observations of 



WlLLEMOES-SUHM (No. 100). 



Penaeus, like the Euphau- 

 aidae, leaves the egg as a true 

 Nauplius (Fig. 122 A). The 

 long, pear-shaped body is still 

 without a shell-fold, and ter- 

 minates posteriorly in two 

 long, furcal setae. At the 

 anterior end of the body, the 

 Nauplius eye is visible. The 

 three typical pairs of Nauplius 

 limbs are still unjointed, and 

 are provided with swimming 

 setae. 



The succeeding Metanauplius 

 stage, in outward appearance, 

 still greatly resembles the Nau- 

 plius, but is distinguished from the latter by the appearance of a 

 transverse dorsal integumental fold (rudiment of the dorsal shield) 



Fig. 122.— Two stages of development of Penaeus 

 (after F. Muller, from Lang's Text-book). 

 A, Nauplivs. B, Protozoaea. 1, first, 2, 

 second antenna ; 5, mandible ; 5, second 

 maxilla ; /, first, II, second maxillipede ; 

 (III-VIII), rudiments of the third to eighth 

 thoracic segment; ab, abdomen. 



