178 HOMOLOGY 



outside on the basal segment of the fourteenth appendage (Fig. 

 68, 14). From this opening the spermatozoa, packed together 

 in bundles called spermatophores, are caught by the tubular 

 exopodites of the fifteenth pair of appendages and placed on 

 the genital groove of the female during copulation. 



The ovaries are similar in general shape and in position, but 

 are bright orange in color and the female gonoduct or oviduct, 

 while it originates in the same relative position, opens to the 

 outside on the basal segment of the twelfth appendage. The 

 eggs are fertilized as they pass out and are covered with a 

 gelatinous mucus by which they stick to the hairs bordering the 

 swimmerets. Thousands of them become thus attached to be 



swayed back and forth by 

 the movements of the 

 swimmerets during the 

 early stages of develop- 

 ment. 



DEVELOPMENT AND 

 METAMORPHOSIS. T h e 

 development of the earth- 

 worm as of hydra, begins 



FIG. 77. A typical nauplius larva of the cop- with the division of the 

 epods with three pairs of appendages. . J 



egg cell into two cells or 



blastomeres, each with one-half of the fertilization nucleus. 

 Development of the lobster begins with the division of the 

 nucleus without division of the egg substance. The second, 

 third, etc., up to the eighth division are the same, a mul- 

 tinucleated cell resulting in which the nuclei arrange them- 

 selves around the periphery of the egg. Then the outer 

 zone of protoplasm divides around each nucleus, the cleavage 

 planes passing radially toward the egg center (Fig. 76). This 

 type of cleavage is characteristic of the arthropods and is called 

 meroblastic as opposed to holoblastic. The yolk is collected in 

 the center of the egg which for this reason is called centrolecithal. 

 Metamorphosis. In the more generalized types of Crustacea 

 this method of cleavage leads to the formation of a free living 

 embryo or larva termed the nauplius. This larva has little 



