COLLECTING AND TRESERVINO MATERIAL. 175 



clams, snails, and slugs should be collected and pre- 

 served in four per cent formalin. A supply of shells 

 should be kept for the purpose of identifying the 

 principal parts before beginning to study the struc- 

 ture of the body. 



Starfish must be procured from the seashore. 

 They are usually preserved in formalin, and will 

 keep indefinitely. The usual cost is about two dol- 

 lars per dozen. 



Fresh-water sponges must be collected late in 

 the fall ; September and October are the best months. 

 Until this season, the gemmules are not matured and 

 the growth has not reached its maximum. For most 

 purposes it is sufficient to dry them and then preserve 

 them from the dust in boxes. To study the flesh and 

 cellular structure, they should be preserved in forma- 

 lin or very strong alcohol. Absolute alcohol is the 

 best preservative of sponges when careful dissection 

 is intended. Sponges should be dropped into abso- 

 lute alcohol as soon as collected. 



Hydras, daphnia, cypris, cyclops, vorticella, 

 paramcecium, stentor, and amceba would better be 

 obtained in a fresh condition. This means that, as a 

 general thing, these animals would better be studied 

 in the spring or in the fall. Aquaria once stocked 

 with them and kept in the schoolroom will usually 

 furnish a fairly good supply of one or all of these 

 forms. A jar, with a handful of hay put into it and 

 let stand from year to year, will usually show 

 several forms of protozoa, including vorticella and 

 paramcecium. 



It is better to keep all aquaria covered. - This 

 prevents the growth of a screen of bacteria which is 

 destructive to most other life in the aquaria. If this 

 be done, the water will not need any changing. 



Pupils should be encouraged to collect their own 

 material and material for the class whenever possible. 



