110 Dr. F. Miiller on the Metamorphoses of the Prawns. 



the frontal margin even in the oldest Nauplius. They appear at 

 first as delicate, nearly globular, limpid vesicles (fig. 3o), but 

 subsequently as minute, firmer, and more opake mammiform 

 appendages to the anterior margin of the ocular peduncles 

 during the whole period of larval life (fig. 80). 



The new segments, on which the thoracic and abdominal feet are 

 afterwards developed, form at first an unjointed, soft, short zone, 

 which, however, soon becomes elongated.- Before this zone at- 

 tains the length of the section of the body lying behind it, a 

 division into eleven segments may be detected, although at first 

 this is not very distinct. At first these segments are of nearly 

 equal length, or the anterior ones may even be longer and more 

 distinctly separated ; but towards the end of this period the five 

 posterior ones form about one-third of the entire length of the 

 body, whilst the six anterior scarcely constitute one-ninth of it, 

 the remainder of the length being half before and half behind 

 these new segments*. The five posterior new segments (abdo- 

 minal segments) acquire a short spine at the hinder margin in 

 the middle of the back, and the last of them also one on each 

 side. Of internal parts, only the intestine is at first clearly 

 distinguishable in these new segments; the ganglionic chain 

 is afterwards developed, and it is only towards the end of this 

 period that the muscles become separated into sharply defined 

 bundles. 



The new appendages sprout from the ventral surface of the 

 corresponding segments at first in the form of simple lobes, 

 which, however, soon show a longer external and shorter internal 

 branch. At first, and indeed when the separation of new seg- 

 ments just begins to be perceptible, the third pair of footjaws 

 and the lateral laminae of the caudal fan are produced; at a 

 much later period the five pairs of thoracic feet make their ap- 

 pearance at once. Before the conclusion of this period, the 

 branches of the footjaws acquire fully developed setae, but still 

 remain unjointed ; the thoracic feet continue rudimentary and 

 destitute of setse. The lateral caudal laminae which are attached 

 directly (without a joint) to the basal joint, acquire a few short 



* Whether the first of these eleven rings is already present (as I believe 

 to be the case) at the commencement of this period — in other words, 

 whether all the eleven, or only ten, segments are really to be indicated as 

 new — I must leave undetermined. In the latter case, we should have, — 

 in the first period (Nauplius) five original segments (antennae, mandibles, 

 tail) and the formation of five new ones (for the maxillaj and footjaws) ; 

 in the second period (Zoea) the formation of 2 X 5 new segments, of which 

 some (thoracic segments) acquire rudimentary feet in this period, and the 

 others (abdominal segments) only in the third period (My sis-form). This 

 simple relation, however, so far from applying generally, would not even 

 suit all the species of the genus Peneus. 



