AND THE DEVELOPMENT OF THE MYRIAPODA. Ill 



the distance between the inflected head and tail of tlie embryo, the body of which 

 was composed entirely of cells, a little larger, and more closely aggregated together 

 than in the preceding examination; but there were no rudiments of limbs, or even 

 of a division of the body into distinct segments. The shell had acquired more firm- 

 ness, but the egg still contracted, and dried up quickly when exposed to the air for 

 a few minutes. On the following day, the twentieth from the deposition of the 

 egg, the outline of the embryo was more apparent (fig. 3.), and on its concave, or 

 ventral surface, there were faint traces of a division of the body into six segments. 

 Up to this period I was unable to detect any funis or umbilical cord to the embryo, 

 a structure of which I was particularly in search, and which I was aware had been 

 seen by Rathke in Crustacea. When the egg was examined in rectified spirit, the 

 outline of the embryo was rendered more distinct, especially at its extremities, and 

 its whole body was contracted so as to leave a space between it and the shell. It 

 was still formed of cells of different sizes. From this time, to the bursting of the 

 shell, the egg became every day larger, until the morning of the 31st of March, the 

 twenty-fifth day from the deposition of the egg, when it was greatly distended, and 

 began to assume a kidney-shaped appearance (fig. 4.) ; that side of it which corre- 

 sponded to the ventral surface of the embryo then became a little concave, and the 

 opposite, which corresponded to the dorsal surface, much more convex. The shell 

 was now bursting longitudinally in the median line of the dorsal surface, and the 

 back of the soft and perfectly white embryo was gradually pressing through the 

 opening. The young being was now entering a new state. Its body had exhausted 

 the nourishment supplied to it by the yelk, and it had thus arrived at the termina- 

 tion of the first period of its development, a period of twenty-five days. 



In the second period of development the embryo is exposed to a new medium, and 

 perhaps derives the means of its further growth from external sources, although it is 

 still enveloped in the fcetal membranes, and retains its connexion with the shell. 



The apodal condition of the young lulus at the bursting of its shell, has already 

 been noticed by Savi and Waga, the latter of whom refers also to its extremely deli- 

 cate and motionless state ; but both of these naturalists have overlooked the remark- 

 able fact of its remaining for many days connected to the shell by means of a distinct 

 funis (c?), and also of its being still inclosed in the amnion, the proper foetal covering. 



The liberation of the embryo by the bursting of its shell is a remarkably slow pro- 

 cess, as compared with the escape of other animals from the egg. In my observa- 

 tions from ten to twelve hours elapsed before the body of the embryo was so far libe- 

 rated as to remain only partially inclosed between the two halves of the shell (fig. 5.), 

 to the interior of which it was still attached by its pedicle or funis (rf). So remarkable 

 is its condition at this period, that it strongly resembles the expansion of the germ 

 in the seed of a plant, rather than the evolution of a living animal. The embryo is 

 perfectly motionless, and the bursting of its shell appears to be effected, not by any 

 direct effort of its own, since, up to this period, it has acquired only the form and 



