1 18 University of California Publications. [zoology. 



The cell layers which make up the body wall of a colony may 

 be distinctly seen in section. PI. XII, Fig. 2, represents a 

 section from a growing tip of a male colony, in which the outer, 

 or ectodermal layer consists of small rounded cells (ec. els. ) , while 

 the inner or mesodermal layer consists of much larger cells 

 possessing a distinct large nucleus (mes. els.). It is part 

 of this inner layer which becomes modified into a germinal 

 epithelium, (ger. els.), and from which both ova and sper- 

 matozoa originate. PI. XII. Fig. 3, is a section from the same 

 series representing much the same characters. If these two 

 sections be compared, the mesodermal cells in each (mes. els.) 

 are seen to be of various sizes. Many are of normal size 

 (mes. eh.), while others are much larger, and constitute the 

 cells of the male germinal epithelium {ger. els.). In the 

 germ cells, the nucleus and nucleolus have increased in size, 

 and are surrounded by a layer of finely granular cytoplasm. 

 The mesodermal cells which go to form the parietal layer are 

 of various sizes and shapes, but of similar appearance. The 

 ectodermal cells are either rounded or elongated, depending upon 

 the portion of the tip in which they are. Near the edges, right 

 and left, they are round, while near the middle they become 

 much elongated and less numerous, (PI. XII, Figs. 10 and 

 11, ee. els.) . 



The relation between the polypide buds and the germinal 

 tissue is shown in Fig. 4, a section from a male colony which 

 represents several stages in the development of the polypides. 

 At the anterior edge, in the angle toward the left (/.) the 

 germinal cells may be seen (ger. els.). Proximal to this point, 

 a mass of cells represents the youngest polypide bud (pd. bd. ~'), 

 and below this there is an older bud (pd. bd. 1) in which the 

 cavity of the stomach is formed (st.) . As the distal portion of 

 the branch continues to grow, the fully formed germinal cells 

 are left behind at or near a point where a polypide bud forms, 

 and in a male colony a few of these cells become attached to 

 each bud constituting the testis of the developing polypides. In 

 PI. XII, Fig. 4, a number of large cells closely resembling the 

 cells of the germinal tissue in size and appearance of the nucleus, 

 are attached to the stomach of the older polypide bud (pd. bd 



