396 DECAPODA. 



The peculiar larval form of the Loricata (Scyllarus, Palinurus) has long 

 been known under the name Phyllosorna (fig. 222 C), but its true nature was 

 first shewn by Couch (No. 474) [Couch did not however recognise the identity 

 of his larva with Phyllosoina ; this was first done by Gerstacker] and shortly 

 afterwards by Gerbe and Coste. These observations were however for a 

 longtime not generally accepted, till Dohrn (No. 477) published his valuable 

 memoir giving an account of how he succeeded in actually rearing Phyllo- 

 soma from the eggs of Scyllarus and Palinurus, and shewing that some of 

 the most remarkable features of the metamorphosis of the Loricata occur 

 before the larva is hatched. 



The embryo of Scyllarus in the egg first of all passes through the 

 usual Nauplius stage, and then after the formation of a cuticle develops an 

 elongated thoracico-abdominal region bent completely over the anterior 

 part of the body. There appear moreover a number of appendages and 

 the rudiments of various organs ; and the embryo passes into a form 

 which may be described as the embryonic Phyllosonia stage. In this stage 

 there are present on the anterior part of the body, in front of the ventral 

 flexure, two pairs of antennae, mandibles, two pairs of maxillse, the second 

 commencing to be biramous, and a small stump representing the first pair of 

 maxillipeds. The part of the body bent over consists of a small quadrate 

 caudal plate, and an appendage-bearing region to which are attached an- 

 teriorly three pairs of biramous appendages the second and third maxilli- 

 peds, and the anterior pair of ambulatory legs and two pairs of undivided 

 appendages the second and third pairs of ambulatory legs. In a slightly 

 later stage the first pair of maxillse becomes biramous, as also does the first 

 pair of maxillipeds in a very rudimentary fashion. The second and third 

 pairs of ambulatory legs become biramous, while the second and third max- 

 illiped nearly completely lose their outer ramus. Very small rudiments of 

 the two hinder ambulatory legs become formed. If the embryo is taken at 

 this stage (vide fig. 222 A, which represents a nearly similar larva of Pali- 

 nurus) out of the egg, it is seen to consist of (1) an anterior enlargement with 

 a vaulted dorsal shield enclosing the yolk, two stalked eyes, and a median 

 eye ; (2) a thoracic region in which the indications of segmentation are 

 visible with the two posterior pairs of maxillipeds (mxp 2 and mxp 3 ) and 

 the ambulatory legs (]) } ) ; (3) an abdominal region distinctly divided into 

 segments and ending in a fork. 



Before the embryo becomes hatched tlie first pair of maxillipeds becomes 

 reduced in size and finally vanishes. The second pair of maxilla? becomes 

 reduced to simple stumps with a few bristles, the second pair of antenna; 

 also appears to undergo a retrogressive change, while the two last thoracic 

 segments cease to be distinguishable. It thus appears that during em- 

 bryonic life the second pair of antennae, the second pair of maxillse, and 

 the second and third pair of maxillipeds and the two hinder ambulatory 

 appendages undergo retrogressive changes, while the first pair of maxillipeds 

 is completely obliterated ! 



The general form of the larva when hatched (fig. 222 B) is not very 

 different from that wh'ch it has during the later stages within the egg. 

 The body is divided into three regions: (1) an anterior cephalic; (2) a 

 middle thoracic, and (3) a small posterior abdominal portion ; and all of 

 them are characterised by their extreme dorso-ventral compression, so that 

 the whole animal has the form of a three-lobed disc, the strange appear- 

 ance of which is much increased by its glass-like transparency. 



