176 Transactions of the Society. 



content ; it becomes conscious of the coming crisis, draws in its head 

 and foot, rounds its trunk into a ball, secretes round itself a gelatinous 

 covering, and waits for better times. 



But the Rotifera owe their wide dispersion not only to the ease 

 with which their eggs are blown from one place to another, but also 

 to their powers of endurance, and to their marvellous capacity for 

 adapting themselves to new surroundings. A Philodine may say 

 with Howell, " I came tumbling out into the world a true cosmo- 

 polite." I have already noticed how the Philodinidse will endure such 

 extremities of heat, cold, and dryness as Nature inflicts on them ; but 

 she does not put their full powers to the test ; for, when time is given 

 to them to don their protective coats, they can bear a heat gradually 

 advancing to 200° Fahr., or a 50 days' exposure to a dryness produced 

 over sulphuric acid in the receiver of a good air-pump. Ehrenberg 

 tells us that whereas he killed Volvox glohator with one electric shock, 

 it took two of the same intensity to kill Hydatina senta ; and that 

 'Rotifer vulgaris will swallow laudanum and " yet be lively ;" adding 

 that a solution of Cantharides seemed " to give it new life." The 

 same irrepressible creature will flourish in water containing a percep- 

 tible quantity of sulphuric acid ; while Asplanehna priodonta will 

 swim about actively for twenty-four hours in a weak solution of 

 salicylic acid ; and Synchseta jpectinata will do the same in chromic 

 acid. The great majority of the fresh-water species die when 

 dropped into sea water, but some will bear sudden immersion in a 

 mixture of one part sea water to two fresh. We should not be 

 surprised, therefore, to find not only that there are thirty-four known 

 marine species of Eotifera, but that seventeen of these species are to 

 be met with alike in salt water and in fresh. 



The following is the list of Eotifera found in salt or brackish 

 water; those marked with a star are also the inhabitants of fresh 

 water. 



Floscularia campanulata.* 

 Melicerta tuhicolaria.* 

 Rotifer citrinus* 

 Synchs&ta Baltica. 



„ tremula (?).* 



Pleurotrocha leptura (?).* 

 Notommata Naias* 

 Proales decipiens* 

 Furcularia forficula* 



„ gracilis.* 



„ Reinhardti. 

 Diglena catellina* 



„ grandis.* 

 Distemma raptor. 



,, marinum, 

 Rattulus calyptus. 

 Monostyla quadridentata. 



Colurus amhlytelus. 

 „ caudatus,* 

 „ dactylotus. 



„ uncinatus.* 

 Mytilia Tavina. 

 Pterodina clypeata. 

 Brachionus Bakeri.* 

 „ Miilleri. 



Notholca striata * 



„ spinifera. 



„ inermis. 



„ scapha.* 



„ thalassia. 

 Anurssa valga.* 

 „ hiremis. 

 Hexarthra polyptera. 



Although this is, doubtless, a very imperfect list, still it is sufficient 

 to show how these fresh-water animals are slowly spreading into the 

 tide pools on the sea-shore. Some may have commenced their change 

 of habitat in the field drains, which are periodically invaded by the 



