ART. 7. STUDIES ON LARVAE OF CRABS — HYMAN. 



METAMOEPHOSIS. 



The complete history of metamorphosis has not been followed in 

 any species. The present paper carries the description of the first 

 two zoeal stages of P. osireum while Smith describes the transforma- 

 tion of the last zoeal stage into a megalops in P. chaetopterana and 

 Faxon the transformation of the last zoeal stage directly into the 

 young crab in P. sayana. When these observations are considered 

 together, it seems probable that the Pinnotherids have at least three — 

 probably four — zoeal stages followed either by a megalops and then 

 the young crab or else by the crab stages directly. This generalisa- 

 tion must be put forward with considerable reserve as it is known 

 that, among the Crustacea, closely related species of the same genus 

 may present developmental histories that are quite different. 



PINNOTHERES OSTREUM Say. 



The zoeas of this species are among the most abundant in towings 

 taken at Beaufort. They are recognised at once by the absence of 

 the spines of the carapace. They are comparatively small and are 

 active and rapid swimmers. When they come into contact with 

 other bodies, the abdomen is flexed under the cephalothorax and the 

 larva forms an almost perfect sphere. All of the appendages are 

 covered except the maxillipeds. 



Cephalothorax. — The dorsal and lateral spines of the carapace are 

 wanting and the rostral spine is reduced to an exceedingly minute 

 tubercle (fig. 1). The eyes are large and well-developed. 



Cephalic appendages. — The antennulefs are very minute and are 

 carried folded imder the anterior border of the carapace so that 

 usually only the terminal hairs are seen (fig. 5). The antennae are 

 still more minute. They may be discovered after careful dissection. 

 The mandibles, maxillules, and maxillae are of the usual brachyuran 

 type (figs. 7, 9, 11). 



Thoracic appendages. — The endopodite of the first maxilliped is 

 composed of five segments. The sensory hair on its terminal segment 

 is very small and is not plumose. The endopodite of the second 

 maxilliped has two segments (figs. 13 and 15). 



Abdomen. — The segments of the abdomen are progressively 

 flattened and broadened as they approach the broad, plate-like 

 telson. The posterior border of the telson is produced into three 

 deltoid teeth. The marginal spines lie between the median and 

 lateral spines (fig. 17). 



FIEST ZOEA. 



The first zoea has been described by Birge in a brief note. He 

 gives accurate outline drawings of the zoea and its appendages. 

 This stage is readily distinguished by the four swimming hairs at 



