3 o o THE NA TURE- S TUD Y RE VIE W [ 2 : 9 - dec. , i 9 o 6 



the embryo extended over one half of the egg, the fifth and sixth 

 the slow perfection of an embryo ready to hatch. 



The younger, smaller, females often lay later than the older, larger 

 ones and if several females of different sizes have laid, the chances 

 will be better for an extension of the hatching period over hours when 

 the pupils may be on hand to see the actual hatching process. When 

 it is seen that a few eggs have changed to fluffy, pink masses, one of 

 the abdominal appendages may be cut off with its load of eggs and in 

 a watch-glass some of these eggs may be seen to let out very slowly 

 the imprisoned young. 



During some days the pupils will have ample opportunity for try- 

 ing to find out how the young after hatching become connected to the 

 parent and what their condition of development, as compared with 

 the adult, really is. Ultimately the young will leave the parent but 

 there is a long and most interesting period of association of mother 

 and offspring that may profitably be studied by the student from a 

 standpoint like that taken by Roesel von Rosenhof in 1755, or if the 

 teacher will so have it, from a more fashionable standpoint of "trop- 

 isms." 



The active larvae are extremely attractive under the lens and for 

 that vast majority of pupils who cannot hope to see living pelagic 

 organisms these crayfish larvae in their brilliant pigmentation and 

 translucency may well serve as a convenient substitute. 



Once the young begin to make extensive excursions away from 

 their mother's apron strings, fine wire net must be used to prevent 

 their loss in the overflow of water. Whenever the mother is fed the 

 conduct of the young should be observed and the large problems of 

 interrelation of parent and offspring considered. 



If well fed the young will shed their shells from time to time and 

 measurements of growth at these times may well be made. 



Questions as to the intelligence, instincts, education of the young, 

 naturally arise and experiments may be devised to limit one's 

 ignorance. If it is desired to keep the young isolated from association 

 with others and to show their innate acts the eggs may be removed 

 before hatching and pinned, by the egg stalk, to floating corks in 

 running water where they will hatch out alone and without association 

 with others. 



The larva; may be fed minute pieces of meat with good supplies 

 of water plants and of ooze to choose from. The red tailed oligochaete, 

 so common in polluted streams, may be kept in stock and will furnish 

 a food-supply much appreciated by the young crayfish. 



