"The funis enters the body of the embryo at the posterior part of the dorsal surface of the future penultimate segment, where the mucro or spine exists in the adult animal, and not at the dorsal surface of the thoracic region, as seen by Rathke in the Crustacea. The proper anal or terminal segment is, as yet, but im perfectly developed. In the funis (d), I also observed some exceedingly delicate struc tures that exhibited all the appearance of vessels. They seemed to enter the body by two sets, that were spread over and entirely lost in the membrane (e). Whether these were indeed vessels, or merely folds of the mem brane I am not certain. The membrane (e) in which they appeared adheres closely to the shell and retains the embryo in connection with it by means of the funis. In the unburst egg, this is also a shut sac like the amnion, and forms the membrane externa or chorion (?), the second or outer investing membrane of the ovum lining the interior of the shell.
"The detection of these two investing mem branes of the embryo in Myriapoda may," says Mr. Newport," be regarded with some interest in reference to the analogies which they bear to similar structures in Vertebrata, since they shew the persistence of one universal law in the mode of development of the germ." On the third day the embryo had consider ably increased in size, but was still perfectly motionless and attached to the shell by the funis. This attachment continues for many days, during which the embryo remains par tially protected by the two halves of the shell. When examined at this period in the recent state, all the parts of its body are still indis tinct, but in specimens that have been for some time in 'spirits of wine, the divisions between the segments are well marked. The rudiments of the legs are more developed, but those of the second and third segments less than the fifth, so that not only at the bursting of its shell, as noticed by Sari, but also for several days afterwards the embryo is competely apo dal, the future limbs existing only in a rudi mentary state. Posteriorly to the fifth segment, the body is more soft and delicate, and the seg ments less clearly defined. This results from the circumstance that it is at this part of the body that the future new segments are to be produced.
On the fourth day, Mr. Newport first ob served some faint traces of a single eye, or ocellus, on each side of the head. The embryo had now further increased in size, and the ru diments of its future legs had become larger and more obtuse, an appearance which the newly-formed limbs of the Articulata often exhibit previously to their further elongation. Traces of the formation of internal organs were now evident through the tegument at the pos terior part of the body, and the funis was con tracted as if about to separate. Internally the body was still formed of cells aggregated toge ther, but differing more in size than at any previous period, as if they were becoming fused into separate tissues, and in the midst of them and closely surrounded on all sides was the newly-formed alimentary canal. The canal was now more opaque, and when pressed out of the body more firmly adhered together than any other internal structure, and was dis tinctly composed of an aggregation of very minute cells. Around the sides of the body
muscular structure was also in the course of development, but as yet was exceedingly in distinct, insomuch that Mr. Newport could discover no perfect fibre, a fact that sufficiently accounts for the entire absence of spontaneous motion in the embryo up to this period.
A new process was now about to commence —the development of new segments. On the third day, as has been already stated, the pos terior part of the body is less distinctly divided into segments than the anterior, the first five segments being most distinctly marked. The sixth and seventh are now more defined. It is in the membrane"; fig. 321, that connects the seventh with the eighth segment at the posterior margin of which last the funis (d) enters, and which segment is permanent as the penultimate throughout. the life of the animal, that the for mation of new segments is taking place. At this period it is only a little ill-defined space that unites the seventh and eighth segments into one mass, but in proportion as the anterior parts of the body become developed, this part is also enlarged, not as a single structure, but as a multiplication or repetition of separate si milar structures.
On the ninth day the changes have advanced much further (fig. 320); not only have the future new segments become more distinct, but trans verse depressions are also seen on the dorsal surface of the original segments, shewingtheirdivision into double ones, as in the perfect animal. The rudi ments of the legs are now further developed, and their transparent distal extremities are seen through the investing brane applied closely together and extended along the ventral surface of the body, as in the nymphs or pupe of true Insects. The an tennm and ocelli are gore apparent, and the embryo itself has increased at least one-third of its original dimensions. It is still attached by the funis to the shell, but this attachment is daily becoming more fragile, and is now sepa rated by very slight causes. The embryo has thus continued to grow through nine succeed ing days, since the bursting of its shell, without any visible means of nourishment, the nutri ment supplied by the yelk having been ex hausted before that occurrence. Hence it be comes a matter of inquiry from whence it now derives its means of growth ? Whether it has already sufficient materials derived from the egg, and stored up within itself for its future development, or whether the external inclosing membrane may not still contribute to the func tion of nutrition by absorbing fluid condensed from the air of the humid locality ir, which it re sides. The probability of this last supposition, says Mr. Newport, is somewhat countenanced by the fact that I have constantly observed the membranes of the embryo at this period co vered with microscopic drops of fluid, but whether this is fluid condensed on the mem branes from the atmosphere of the dwelling, or whether it results from the transudation of that which was contained in the amnion, re mains for future inquiry.