METAZOA VERMES. 297 



embryos hatch; the pouch then breaks, and the larvae 

 are set free. 



The larva just after hatching (fig. i) has a flattened, 

 unsegmented body which shows no differentiation into 

 regions. Very soon, however, the beginnings of segments 

 (fig. 2) are visible, and the head is marked off by a slight 

 constriction. The segments become more apparent (fig. 

 3) and the three regions are clearly marked (fig. 4). The 

 tentacles bud out (fig. 5) and the bristles grow from the 

 middle region (fig. 6). The tentacles increase in size and 

 the setae in number (fig. 7). Later the posterior organs, 

 known as cirri, grow longer (figs. 8, 9). The mature 

 asexual form, called the "parent-stock," is represented in 

 fig. 10. It multiplies either by division or by budding. 

 If by the former process the anterior end remains asexual 

 while the posterior end develops into either a male (fig. 

 n, male ready to separate from parent-stock; fig. 12, for- 

 ward part of a male) or a female (fig. 13). Larger draw- 

 ings of the mature Autolytus are framed and placed over 

 the Section. The figure on the left represents the 

 asexual parent stock dividing in two; the middle figure 

 is the female with the egg-bag, and the figure on the right 

 the free male. These two sexually mature individuals 

 produce the fertilized egg which in turn develops into the 

 sexless parent stock (fig. 10). The latter produces more 

 than one offspring, for after this has left, the anterior end 

 buds out new segments until a posterior part is formed 

 which in time is ready to be thrown off and to develop 

 into either a male or a female. . 



Autolytus is placed with the free-swimming forms since 

 the adult male and female are found at the surface of the 

 sea. The parent stock also is free-swimming when the 

 sexual individual is attached to it. At other times it 

 makes a delicate tube which it leaves at will. 



The development of Autolytus which we have just traced 

 is exceptional in one particular, namely, in the flattened, 

 unsegmented state of the very young larva. In conse- 



