240 Development Process; Common Shrimp. 



When the process is completed and the young shrimp 

 escapes from the egg, it is then only about -$ to -fa of an inch 

 long. Its combined head and body (cephalothorax) are 

 relatively biggish ; as yet there are no swimmerets ; and the 

 tail ends in a broad, shovel-shaped expansion. It is now in the 

 so-called Zoea-stage of naturalists. These diminutive and 

 larval shrimps, little more than pin-heads in size, are active, 

 free-swimming creatures, which seek and dwell on the 

 surface of the water. (See fig. 28, p. 236, and fig. 29 infra.') 



Development meantime proceeds very rapidly. But it is 

 only after several skin moultings in quick succession, together 

 with outgrowths of appendages and other modifications or 

 metamorphoses, that the little shrimp acquires the adult form.* 



* Ehrenbaum in his researches has minutely described five larval stages, and a 

 sixth when it enters into the complete young shrimp form. His figures, though 

 bearing the stamp of accuracy, unfortunately, are not well adapted for unscientific 

 readers. Since our report has been in the printer's hands, Williamson, of the Aberdeen 

 Laboratory, Scotch Fishing Board, in the 19th Ann. Rep. for 1900 (1901) has given 

 further additions to, and confirmatory of Ehrenbaum's work. He traces with elaborate 

 detail the development of the several head, body and tail appendages, and copiously 

 illustrates the same. For our purpose we limit notice to those figures exhibiting the 

 general aspect of the temporary surface resident larva? and early ground residents. 

 Williamson's delineations being irregularly dispersed in his plates may fail to attract 

 the attention they deserve. We here reproduce them about half the size of his 

 drawings, and rearranged in the manner subjoined, for more ready comparison of 

 changes incident to each moulting stage. 



FIG. 29. 



Brown Shrimp (Crangon vulgaris). Figs. 1 to 5 (inclusive). Magnified representa- 

 tions of the five larval stages, when minute habitants of top water. They show the 

 progressive changes in head, body and tail appendages after each larval moult 



Fig. 6. In this, the sixth stage, when the creature takes to a bottom lite, the 

 adult characters are obvious, though the appendages are scarcely fully formed. 



Fig. 7. With increase of size and further development of parts, the complete 

 young shrimp condition of the shallows is reached. (Note that Williamson s figs. 1 

 to 3 were drawn to scale x 30, whereas figs. 4, to 7 were only x 12.) 



