of the Fishery Board for Scotland. 



139 



The Larval Stages. 



The Larval stages of this form are divisible into three groups : (1) 

 the Protozoea stage : (2) the Zoea stages, four in number : (3) the 

 Megalops stage. 



Protozoea (Fig. 160). 



The so-called Protozoea stage was described by Du Cane, Spence 

 Bate, and other authors. It is of very short duration. The larva 

 leaves the egg capsule in the condition shown in the figure. It has 

 neither the rostral nor dorsal spine. It immediately casts its delicate 

 integument and appears as a Zoea of the I. stage. 



I have not noticed the Protozoea stage in cases where the larvae 

 have hatched out in a tank. It may however be got by washing the 

 egg- mass of a female during the time the young are hatching. 



Faxon* gives a correct description of this stage, and it is not 

 necessary here to recapitulate it. 



The Zoea. 



The Zoea is wholly pelagic. 



It is a feeding period during which the Pereiopods and Pleopods 

 develop. 



Functional Appendages. The Zoea has a cephalothorax, and abdomen 

 and telson. There is no sharper dividing line between the cephalon and 

 the thorax than there is in the adult. The thorax is only partly 

 developed, two thoracic appendages alone being functional, viz. the First 

 and Second Maxilli pedes. The hind part of the thorax, to which 

 pertain the Third Maxillipede and the five Pereiopods, is rudimentary. 



The cephalic appendages are all present and functional : they are the 

 Eye, Antennule, Antenna, Mandible, First Maxilla, Second Maxilla. 



The abdomen is 5-jointed ; the pleopods are rudimentary. 



All the functional appendages differ very much from their structure 

 in the adult. 



With the exception of the telson they are feeding and sensory organs. 



The telson, as Du Cane pointed out, functions mainly in assisting the 

 ecdysis of the integument of the appendages. {Cp. the telson in the 

 Zoea of Cra7igon vidyaris.) The abdomen and telson are also used for 

 intermittent progression. The principal motor organs are the setose 

 exopodites of the first and second maxillipedes. 



The Megalops, 



The Megalops is the connecting link between the pelagic Zoea and 

 the demersal young crab. It partakes of the characters of both. It 

 swims by means of its five pairs of pleopods, after the manner of a 

 Crangon, and also crawls about on the bottom by means of its 

 pereiopods. 



In Crangon the Megalops stage persists with slight modifications to 

 be the adult condition. The Brachyura pass through a Crangon stage in 

 the Megalops, and then undergo further specialisation which affects the 

 abdomen alone. The pleopods change in character, they lose the 



* "On some Points in the Structure of the Embryonic Zoea [Carcinus timnas and 

 Panopeus Sayi]," Bull. Mm. Compar. Zoology, Harcardy vol. vi., No. 10, 2 pi., p. 159. 

 Cambridge, Mass., U.S.A. ; 1880. 



