APPENDIX 



Tho development of the pilchard egf^ was separated into eleven stages 

 during the investigation of pilchard spawning, a brief description of 

 each of which follows e 



Stage I 



In stage I v;ere included all pilchard eggs that were not undergoing 

 development, either because they vj-ere so recently fertilized that cleavage 

 had not yet begun or because they vrere unfertilized. Pre-cleavage eggs 

 are usually smaller in size than are pilchard eggs undergoing devclopmentj 

 the difference is not in the yolk mass, Virhich is fully as large in the 

 pre-cleavage eggs, but in the width of the perivitelline space, which 

 nay be nearly wanting. Ilany eggs in this stage have an accumulation 

 of protoplasm at the animal pole to form a blastodisc. 



Stage II 



The period of development of the blastodermal cap is covered in 

 stage II. Although this stage includes the early cleavage divisions, 

 no pilchard eggs have been observed in our samples v>rith fevirer than about 

 128 cells. The lack of material shoviring early cleavage divisions is hard 

 to explain, ^specially since stage I eggs were taken previous to initiat- 

 ing cleavage. Such divisions must take place very rapidly, indeed. 

 While the individual cells arc fairly large and quite evident, the blas- 

 todermal cap has a rugged, berry-like appearance. As the cells become 

 minute and indistinct through repeated divisions, the cap assumes the 

 shape of a smooth, roimdcd, lenticular dome. The pilchard egg floats 

 with the blastodermal cap dovmwards. At the opposite end of the yolk 

 mass is the single, large oil globule. This stage persists until seg- 

 mentation cavity is formed. 



Stage III 



Stage III covers the period of development from the first appearance 

 of the segmentation cavity to the definite establishment of the embryonic 

 shield. The segmentation cavity is formed v;hen the blastodermal cap sepa- 

 rates from the underlying periblast in the middle portion of the cap; 

 the' cavity forms soraev/hat eccentrically, leaving the blastoderm on one 

 side of the cavity somev/hat thicker than elsewhere. The thickened area 

 is the; region of the developing' embryonic sheild. However, the outline 

 of the embryo is not definitely defined in this area until after this • 

 stage. The germ ring begins the envelopment of the yolk v/ith a cellular 

 sheathj by the end of the stage the ring has enclosed a third of the 

 yolk mass, 



Stago iV 



This stago begins whon the general outline of tho embryo can be dis- 

 cerned along the median line of the embryonic shield. Tho germ ring at 

 the beginning of the stage encloses a third of the yolk mass; the end-point 



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