212 THE entomologist's record. 



The primitive ovary is composed of a mass of cells, which after a 

 time become covered with a coating of connective tissue. The cells 

 are then said to fuse to form what is called a syncytium. To learn the 

 earliest condition of the egg, it is almost certainly necessary to examine 

 the structures forming the ovaries present in the pupal or even larval 

 stage. 



In the ovaries of butterflies there would appear to be, besides the 

 cells that form the syncytium, three other kinds of cells — the egg- 

 cells proper, epithelial cells, and nutritive cells. At the time of 

 emergence of the butterfly from the chrysalis, the ovarioles are well 

 developed, and consist of long slender filaments made up of divisions 

 which have been called " oval units " or " egg-chambers." Those egg- 

 chambers nearest the external portion of the ovary are larger than those 

 which are more interior, and the egg^-cells in them can be distinguished 

 from the epithelial and nutritive cells by their better-developed nucleus 

 and nucleoli. 



An egg-chamber is formed by the rapid multiplication of epithelial 

 cells, forming columnar stnictures surrounding the egg - cell. 

 When the egg-chamber has increased to almost the size of a fully- 

 formed egg, the egg-cell commences to grow rapidly at the expense of 

 the epithelial cells, Avhich surround it and form the egg-chamber, the 

 latter being finally reduced to a ]iractically infinitesimal quantity of 

 waste. The ni;cleus in the egg-cell also grows rapidly, and occupies a 

 position on one side and near the upper end of the cell ; it has a dis- 

 tinct nucleolus. As the egg approaches maturity tlie nucleolus dis- 

 ajDpears in the nucleus, the latter also afterwards disappearing and 

 apparently diffusing itself in the yelk. 



The egg is now really a mass of yelk, surrounded and embedded in 

 living protoplasm ; then another nucleus is developed and forms the 

 female pronucleus, which also is surrounded liy protoplasm. This at 

 the time of fertilisation sinks into the yelk. The pronucleus and the 

 protoplasm subdivide into cells each with a nucleiis and plasma, and 

 the surrounding yelk is used as food. The increase and development 

 of these cells continue Avith the consequent degeneration and absorption 

 of the yelk. There appears to be a certain amount of analogy between 

 the breaking up of the yelk and its consequent destruction as such, 

 together with the building up of nucleated cells therefrom, and the 

 histolysis of the pupal tissues. 



9. — On the development of the embryo in the egg. — At the time 

 that the egg is laid the main mass of it is made up of yelk-spherules. 

 These spherules become granular, and the granules gradually replace 

 the spherules and are themselves again changed into yelk-cells, the 

 probability being that they are thus changed in order to form suitable 

 nourishment for the young embryo. At this time the newly-formed 

 blastoderm-cells begin to pass towards the circumference, leaving the 

 degenerated yelk-cells in the centre. In addition to these yelk- 

 spherules, the egg contains a homogeneous fluid which has the ordinary 

 composition of proto])lasm, and consists essentially of the chemical 

 elements — carbon, hydrogen, oxygen and nitrogen. The great charac- 

 teristic of this protoplasmic fluid is its vitality, its abilit}^ to break up 

 and sub-divide, to develop cellular structure, and to build up tissue from 

 the cells produced by cell-division. After fertilisation the protoplasmic 

 fluid inside the ovum remains in a homogeneous condition for a certain 



