40 J. T. PATTERSON 



3. The egg may be placed in any part of the host egg, but does 

 not develop unless embedded in the tissues of the host embryo 

 or larva. 



4. The freshly laid egg is pear-shaped, and contains, in addi- 

 tion to the nucleus, a large nucleolus. The broad end of the egg 

 is posterior and the narrower end anterior. 



5. In fertilization only a single sperm enters. Polyspermy 

 never occurs. 



6. The maturation divisions are typical, and result in reduc- 

 ing the number of chromosomes from sixteen to eight. The 

 polar body chromosomes do not form nuclei, and hence are not 

 accompanied by cytoplasmic segmentation. Two of the three 

 groups of polar body chromosomes fuse to form a polar nucleus; 

 the third disintegrates. 



7. The egg develops whether fertilized or not. If unfertilized 

 it produces a brood of males. Eggs laid by a fertilized female 

 produce mixed broods. 



8. The cleavage nuclei are from the first accompanied by 

 cytoplasmic segmentation. Cleavage is confined to the poste- 

 rior end of the egg, and eventually results in producing a morula- 

 like stage. 



9. The nucleolus is inherited by only one of the first four blas- 

 tomeres. Its history can be traced accurately to the twenty- 

 eight-celled stage, in which its materials are distributed to four 

 cells. There is no evidence indicating that the descendants of 

 these four cells become the germ cells of the sexual embryos. 



10. The polar nucleus divides, forming several nuclei. These 

 with the cytoplasm of the anterior third of the egg flow down and 

 surround the embryonic cells or blastomeres, finally forming a 

 nucleated membrane or envelope. 



11. The morula develops into a polj^germ. which consists of 

 a number (fifteen to twenty) of primary masses. Each primary 

 mass consists of a group of definitive embryonic cells, surrounded 

 by an inner membrane. This membrane is formed from certain 

 blastomeres during the development of the polygerm. 



12. The primary masses multiply by constrictions of the inner 

 membrane, followed by constrictions or ingrowths from the 



