PEEFACE. 



The present Monograph is, with the exception of slight 

 additions and corrections, a reprint of a series of papers which 

 appeared in the Quarterly Journal of Microscopical Science 

 during the years 1885 — 8. 



Owing to the rather long period over which the publication 

 has extended, there is I fear a certain amount of repetition and 

 of irregularity in the arrangement of the matter, for which I 

 must apologise to the reader. I have attempted to reduce any 

 confusion, which may be caused by the latter defect, by a 

 detailed table of contents and by the series of diagrams on 

 PI. XIIL, which will I hope show at a glance the method of 

 development of the chief organs. 



I may take this opportunity of stating that while my 

 series of Capensis embryos is quite complete, there is a 

 considerable period in the development of P. Balfouri of which 

 I have but little or no knowledge. Between the stage of 

 Fig. 12 PI. I. and a stage resembling the Capensis embryo 

 shown at Fig. 26 PI. II., I have only one stage of Balfouri and 

 that of a structure quite unlike anything in the development 

 of the larger species. These embryos (PL I. Fig. 16), of which 

 I have large numbers, appear to consist of a reticular mass of 

 branched cells completely surrounded by a layer of flat cells. 

 The existence of this stage seems to me to indicate that the 

 development of Balfouri between the Umits described above 

 does not take the same course as in Capensis and that an 

 examination of it would prove to be of considerable interest. 



