Dr. F. Miiller on the Metamorphoses of the Praxcns. 113 



length of the apical joint (the moveable finjser) which still bears 

 its terminal bristles. In the fourth and fifth pairs of thoracic 

 feet also, the inner branch is now divided into four joints, and 

 already somewhat exceeds the outer one in length. In animals 

 4*5 mill, long, the fingers of the chelae are of equal length ; on 

 the fourth and fifth pairs of feet an acute process (the claw) is 

 visible beside the terminal setae, and, especially in the fourth 

 pair, the length of the true leg considerably exceeds that of the 

 outer branch. 



The abdomiTuil feet are recognizable as small mammillse even in 

 animals of 2*8 mill, in length ; they are at first simple, and, as 

 in the ca^e of the thoracic feet, it is the outer branch that is 

 first developed. In animals of 4*5 mill, in length, they are 

 already of considerable size, but still without joints or setse, and 

 the inner branch appears only as an insignificant appendage to 

 the outer one. 



The first rudiments of the bronchia are recognizable, in ani- 

 mals bi'low 4 mill, in length, in the form of small roundish 

 excrescences at the base of the footjaws and chelie, and subse- 

 quently also on the fourth pair of thoracic feet. 



From the .Vj/m-like larva of 4*5 mill, in length there is but 

 a small step to the Prawn-form. The youngest animals ob- 

 served in this form were 5 mill. long. Their frontal process had 

 three teeth above. The antennae bad undergone no change. 

 The eyes no luni;er had any appendage : the median eye had 

 become very indistinct. The upper lip had entirely lost its 

 spine, and the mandibular ])al|)i had acquired two joints and 

 short setae. The two anterior pairs of footjaws had approached 

 close to the mouth, and become much shorter than the third 

 pair. The outer branches of the thoracic feet, which are re- 

 tained through life (as the so-called palpus fiagelliformis) in 

 many species of Peneus, had entirely disappeared. The abdo- 

 minal feet had acquired joints and bristles (on the outer branch). 

 The central plate of the caudal fan was diminished posteriorly, 

 and bore on its straight posterior margin ten spines, of which 

 those at the angles were the longest ; on each lateral mai^in 

 there were three shorter spines. The branchiae (one over each 

 fourth thoracic foot, and two over each of the preceding ones) 

 were still elongated laminae with entire margins (they are 

 plumosely cut in animals 9 mill, in length). The liver had 

 begun to acquire a more composite form by the formation of 

 new sacs and the ramification of the old ones. 



The animal was not observed more than 9-10 mill, in length. 



A second larva is readily distinguishable from the preceding, 

 in the later Zoea-form, by the fact that the anterior margin of 

 Ann. &; Mag. N, Hist. Ser.3. Fo/.xiv. 8 



