vol. 3.1 Robertson. — Emdrptttkic Fission in Crista. 117 



dence is less conclusive for this species. Tin* other two, Crista 

 geniculate and Crisia cornuta are probably moneeoious. 



REPEODUCTIVE PEOCESSES. 



si:\i \I, ELEMENTS. 



1. Origin of the M<ii< Genital Products. — Crisia, and perhaps 

 other genera of the Cyclostomata, differ from the rest of the 

 bryozoa in the production of the sexual elements. In young and 

 growing colonies of this genus these products originate and are 

 differentiated as such, at the tips of tin branches. This ran 

 besl lie seen in the spring when the colonies are growing actively, 

 and when the germinal tissue is in the healthiest condition. Dur- 

 ing the fall and winter months the tissue is thin even at the 

 growing points, stains badly, and is in a degenerated state. In 

 the latter part of February and throughout March, April, and 

 May, however, both sorts of germinal cells are abundant, and 

 form very conspicuous objects in all the young tips. The tissue 

 at the growing points at this time forms a thick layer of 

 "embryonic" cells closely packed together and staining deeply 

 in haematoxylin. It is here differentiated into two layers which 

 form the body wall, or lining of the zocecia. PI. XII, Fig. 1, 

 represents the tip of a branch of Crisia eburnea, which has been 

 decalcified, stained ami mounted in toto. It consists of two 



series of ■/. jia (:' and :') lying side by side. At the growing 



point (gr. tis.) the zocecia are cut off alternately from the outer 

 edges, the bases (b.) or proximal extremities of each pair being 

 in contact, while their distal portions arc separated by the bases 

 of the next succeeding pair. The branch is thus somewhat flat- 

 tened, having a dorsal (d.) and a ventral side (v.), and a right ( r. ) 

 and a left (/.(edge. The growing point includes that portion 

 which is anterior to the youngest pair of zooecia and consists of 

 two parts, (") the layers of deeply staining cells {gr. tis.). and 

 (/»). the budding region. This latter is represented in Fig. 1 

 by young polypides (/»/. Int.) in various stages of advance- 

 ment. These portions are again shown in PI. XIII, Fig. 18, 

 which represents the tip of an actively growing branch con- 

 taining, besides a developing ovicell (ovl.), a number of young 

 polypides (//'/. ) . 



