AND THE DEVELOPMENT OP THE MYRIAPODA. 115 



been exhausted before that occurrence. Hence it becomes matter of inquiry, from 

 whence it now derives its means of growth ? Whether it has ah*eady sufficient mate- 

 rials derived from the egg, and stored up within itself for its further development ; 

 or whether the external inclosing membrane may not still contribute to the function 

 of nutrition by absorbing fluid condensed from the air of the humid locality in which 

 it resides ? The probability of this last supposition is somewhat countenanced by the 

 fact, that I have constantly observed the membranes of the embryo at this period 

 covered with microscopic drops of fluid ; but whether this is fluid condensed on the 

 membranes from the atmosphere of the dwelling, or whether it results from the trans- 

 udation of that which was contained in the amnion, remains for future inquiry. 



Up to this period the embryo gives not the slightest evidence of spontaneous or 

 voluntary motion. Internally, it is still composed of cells of different sizes, that are 

 now in the course of producing muscular and other structures. In some parts of its 

 body no arrangement of them seems as yet to have taken place, the cells being merely 

 aggregated together. Cells of three very distinct sizes now exist. The diameter of 

 the largest of these is nearly three times that of the second size ; and the second 

 again are nearly twice and a half the size of the smallest. The smallest-sized cells 

 fill up the interspaces of the others, and appear as if breaking down to form intersti- 

 tial or cellular substance, while the second-sized cells are arranged in rows to form 

 particular structures. In the midst of these cells the alimentary canal is now nearly 

 complete, but I have been unable to observe its connexion with the funis ; and at its 

 anal extremity it is a little dilated, and extends forward as a short straight intestine, 

 the rectuMj until it arrives at a part where a valve seems about to be formed. The 

 diameter of the canal is there enlarged, and on its surface are three distinct longitu- 

 dinal muscular bands. The so-called hepatic vessels also exist as distinct tubes, in- 

 serted, one on each side, into the alimentary canal at the constricted or valve-like 

 part above noticed. The canal is then continued forwards until it is again dilated 

 into the proper stomach, and terminates, or rather commences, in a narrow oesophagus. 

 It is much longer than the body of the embryo, being convoluted or folded upon 

 itself, in its lower portion, to adapt it to the changes the body undergoes in the en- 

 largement and elongation of its segments. It is not yet separated from the now 

 forming structures by any distinct investment, either adipose or peritoneal, except 

 only what belongs to itself; but it is closely surrounded by cells of the second and 

 third size. 



On the tenth day, the great circulatory, or dorsal vessel, was most distinctly seen 

 through the amnion and skin. This doubtless had existed much earlier, although not 

 observed. It was exceedingly well marked, but I was unable to observe any motion 

 in it. The head of the embryo had now begun to assume the peculiar corneous ap- 

 pearance common to the larvae of true insects ; its body had much increased in size, 

 and the amnion was still covered with microscopic drops of fluid. 



On the eleventh day the head was more distinct, and the antennae appeared at its 



MDCCCXLI. R 



