8 THK VorNG or TIIK CKAYFISHES ASTACUS and CAMBAUrs 



made from specimens preserved in alcohol, and, however excellent for their pur- 

 pose, fail to give the .iust proportions of the larvae, since all alcoholic specimens 

 of young crayfish are much swollen and distorted. 



While two more figures of the young crayfish have recently been given, 

 (Andrews, '04) details of external structure are still lacking. 



Having obtained the young of both Astacus and Cambarus by hatching the 

 eggs in the laboratory, it seemed well to fill in some of the gap in our knowledge 

 of the early larval life of crayfish, and especially so as the details of a curious 

 mode of connection with the parent were here first made evident. 



HISTORICAL. 



A l)ri('f statement of the history of our knowledge of the young of crayfish 

 will show that as yet the character of the appendages in the early stages, the 

 exact number of stages present in the life of the young while associated with 

 the niotlier, and tlie nature of the means l)y which the young are held attached 

 to the mother have waited discovery and illustration. 



To Roesel von Rosenhof belongs the credit of an enthusiastic appreciation 

 of tli(> care of the mother crayfish for the young; the observation that the 

 young ai-e transparent and like tlie i)arent; the description of their crowding 

 upon the abdomen of the parent and of their finally foi'saking her after a few 

 days, during which, liowever, they would return to her at times as if recalled by 

 a signal. 



Rathke ('29) was chiefly concerned with the embryology of the crayfish, but 

 also described something of the growth in proportions and in internal anatomy 

 of the young after hatching and gave figures of the embryo and of some of its 

 appendages shortly before hatching. 



Reichenbach ('86) also added to his classic study of the emltryology only 

 a figure of the abdomen of a recently hatched larva. 



Soubeiran ('65) measured young crayfish grown at the farm of (Jlairfon- 

 taine and recorded their moultings and rates of growth. More facts of this 

 .same kind were gathered by Chantran ('70, '71) from prolonged study of larvfe 

 reareil in ijic lal)oratory of M. Coste. Chantran also discovered a peculiar fila- 

 ment that held the young to the egg-shell after hatching and he finally convinced 

 himself that the young ate their egg shells and their cast-off skins. Some 

 other observations upon the size and times of moulting of young crayfish in 

 Sweden were also made by Steffenberg ( '72). 



Huxley ('79) illustiated the recently hatched larva' by two wood cuts, one 

 showing the early larva fastened to the maternal pleopods liy its peculiarly re- 

 curved claws, which he first described and figured, and the other a dorsal view 

 of such a larva. He rectified the previous statement that the young at hatch- 

 ing are exactly like the adult and pointed out their differences in lack of setae. 



