AND THE DEVELOPMENT OF THE MYRIAPODA. 109 



translucent, but soon becomes more opake. Its shell is soft and elastic, and, when 

 exposed to the air, quickly becomes dry and shrivelled. It is on this account very 

 difficult to preserve it to watch the changes in the embryo. Of at least a dozen 

 packets of eggs which I obtained this spring, I have succeeded in rearing only one, 

 which happened to be the packet first deposited, as just described. It is owing, pro- 

 bably, to this difficulty in rearing the eggs and the young of the lulidse, that the 

 changes of these animals have been so imperfectly known, and that so much want of 

 precision has been found in the observations of those who have most attended to this 

 subject. Thus Degeer, who first watched the development of these animals, de- 

 scribes them as possessing six legs when newly hatched*, while M. Savi states that 

 they are completely apodal-f; and WagaJ, in his excellent observations on this 

 class, confirms the statements of Savi, but is exceedingly vague in parts of his ac- 

 count of the changes, and has entirely overlooked many most important facts in 

 regard to the production of the new segments. 



In my own investigations these difficulties were in part guarded against by filling 

 a thin glass tube with moistened clay, in which a little cavity was formed for the 

 eggs close to the glass, and when the eggs had been carefully removed into it the 

 hole was closed up with clay, and also the tube with a cork. By this means the 

 eggs could be watched from day to day, with a common lens, through the glass, 

 without being exposed to the atmosphere. In this way the changes were easily ob- 

 served ; and one or more eggs were removed from time to time for closer inspection 

 beneath the microscope, care being taken always to close up immediately the hole in 

 the clay. The specimens were examined both in the recent state, and also after 

 they had remained a few hours in spirit of wine, so that the changes were accurately 

 noticed. 



The time occupied by the development of these animals extends through many 

 weeks. It is divisible into separate periods, which are most distinctly marked, but 

 the extent of which is influenced by external circumstances; and although in general 

 of a certain duration, it is more or less hastened, as in many true insects, by an abun- 

 dance or deficiency of food, and above all by the temperature of the surrounding me- 

 dium. I have been unable, from accidental loss of specimens, as well as from the time 

 required for their completion necessarily extending far beyond the present period, to 

 observe the whole of the changes as they occur throughout the entire life of the 

 species, but nevertheless have been able to extend my investigations sufficiently far 

 to enable me to record some remarkable facts, the occurrence of which, I have di- 

 stinctly ascertained, continues to the full development of the species, and indicates the 

 existence of one general law or principle in the growth of this class of animals. 



* M^moires, torn. vii. p. 582. 



t Observazioni per servire alia storia di una specie di lulus communissima, ^o/ojfna, 181 7. Bulletin des Sciences 

 Naturelles, torn. xii. Dec. 1823. Memorie Scientificke de Paolo Savi Professore, &c. Decade 1™* Pisa, 1828. 

 X Loc. cit. 



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