AND DEVELOPMENT OF MELOE. 171 



envelope around the nucleus within an adult cell, and this is followed by the fissiparous 

 division of the nucleus itself into two bodies, which, subsequently enlarging, have each 

 their own proper cell- wall formed around them ; after which the cell- wall of the parent 

 structure disappears, and leaves the young nuclei free to be developed into separate cells, 

 like that from which they have originated. Thus the end of the development of a forma- 

 tive cell is the fissiparous division of its nucleus. This mode of development of the tegu- 

 ment in the young animal, after it has left the egg, is confirmatory of the theory of 

 Schwann with reference to that of the general tissues ; and it also accords with the views 

 of Kolliker respecting the division of the yelk cells in the ovum ; and with original obser- 

 vations made by myself, to be elsewhere demonstrated, on the mode of formation of the 

 blastoderma. 



If a transparent portion of the surface of one of the thoracic segments of a young Meloe 

 which has been for some months in strong spirit, be covered with thin talc, with a little 

 fluid around it, and be then examined by transmitted light with a magnifying power of 

 four hundred and fifty diameters, we can immediately recognize the granular, nucleated 

 external cells of the tegument. If then we approach the lens to the object, so as to be too 

 near to have the external cells in focus of vision, the layer of cells beneath them is brought 

 into view. The cells of this deeper-seated layer are smaller than those of the outer one. 

 If the specimen examined has been several days from the egg, before immersion in spirit, 

 then these cells, instead of having each a single granulated nucleus like those of the outer 

 layer, are found to contain each two nuclei of equal sizes, closely approximated together, 

 but perfectly distinct, and inclosed in one common envelope (fig. 8). In some of the cells 

 the two nuclei are more separated than in others, while in those which have most 

 recently changed they are closely approximated. Occasionally the original nucleus of a 

 cell, not yet divided into two, is observed, in the commencement of its change, with a 

 fissiparous emargination on one surface ; but this fact can only be seen when the exami- 

 nation happens to be made on an insect in which the tegument has not far advanced in 

 its changes. The fissiparous division of the nucleus thus appears to be the usual mode of 

 growth of all cellseform tissues. 



Although the solidified tegument supplies the place of a true skeleton in the Articulata, 

 it is also the agent of other functions ; which are of as much importance to the welfare of 

 the animal physiologically, as this is anatomically. It is the medium of the transudation 

 of effete matters from the surface of the body, the retention of which would be detrimental 

 to the entire organism. The cellseform structure of the tegument enables us readily to 

 understand its adaptation to this office. But, besides this, it is subservient to another 

 function, which is equally important with that of transudation, — the aeration or oxygena- 

 tion of the fluids. This is effected solely by the tegument in the very young embryo in the 

 egg ; but as the embryo is advanced to maturity, the function is shared by, and, after birth, 

 is almost entirely performed by respiratory organs, which originate in, and are constantly 

 connected with the tegument as spiracles, or breathing orifices in the sides of the body 

 (fig. 1 b b). 



These respiratory organs are among the last formed of the essential structures of the 

 embryo. I have not been able to detect the existence of spiracles in Meloe until nearly 



