32 



INVERTEBRATE MORPHOLOGY. 



macro- nor microspores develop directly but further develop- 

 ment is contingent upon the conjugation of a micro- with a 

 macrospore. 



In this respect considerable interest attaches to Volvox ; 

 certain cells, usually those situated in the posterior hemi- 

 sphere, enlarge and project into the interior cavity, dividing 



FIG. 16. 1. Phacotus lenticularis ; 2. MACROSPORES AND MICROSPORES OP 



THE. SAME SPECIES (after BUTSCHLI). 

 sch = shell. n = nucleus. 



when they have reached their full growth into a number of 

 cells which arrange themselves in a hollow sphere forming 

 daughter colonies in the interior of the parent. In addition 

 to this a sexual process occurs ushered in by certain indi- 

 viduals gradually enlarging, and leaving their position at the 

 surface of the colony. In the interior some of them continue 

 to enlarge, forming ova (niacrospores), Avhile others divide 

 frequently, forming packets of elongated cells furnished with 

 flagella; these may be termed spermatozoa (microspores). The 

 ova develop into colonies similar to the parent after conjuga- 

 tion with spermatozoa. Since many of the cells of the parent 

 colony do not participate in this reproductive act, but disin- 

 tegrate and die on the development of the daughter colonies, 

 it is clear that we have in this form a rather marked differ- 

 entiation of the individuals of the colony, the individualities 

 of the constituent cells being to a slight extent merged in the 

 individuality of the colony. 



In Noctilnca in addition to simple division a process of reproduction 

 occurs which partakes of the character of budding. It is apparently pro- 



