18 BULLETIN OF THE 



consideration. The ;;«• immediately below it represents the embryonic 

 mass situated at the tip of the stalk, from which all the gemmiparous 

 tissue distributed throughout the stock has taken its origin. As the 

 stalk has grown, there have been left behind the embryonic masses repre- 

 sented by ^. Three of these have arisen together, and the process has 

 been repeated as often as segments have been formed. The separation 

 of the segments is represented in the formula by a dash. Between every 

 two dashes the same budding process is repeated. 



A 



^xb xxa a axx bx:+: 



The median embryonic masses (*) give rise to the individuals a, b, 

 and c, and leave with each a dowry of embryonic tissue represented by x . 

 Each of these individuals a, b, and c, with its embryonic mass x,now 

 acts exactly like A J;C- . Tlie lateral embryonic masses act precisely as 

 do the median ones. 



The typical condition expressed by the foregoing formula is not often 

 perfectly realized, for the simple reason that the stock would thereby be- 

 come too crowded. The more frequent modifications are the absence of 

 the median bud, the Absence of one or both of the lateral buds (stolons) 

 and, occasionally, the apparent substitution of a branch for a stolon. 



The foregoing formula is one of the most complicated that it is neces- 

 sary to make for Bryozoa, for nowhere else are the embryonic masses so 

 abundant relative to the polypides, or, in other words, nowhere else are 

 so many embryonic masses borne by one individual. It is quite com- 

 mon among other species to find three embryonic masses arising from 

 one ; but here the formation of triple masses is repeated as often as the 

 number of segments in the stalk. This fact raises the question of the 

 significance of these segments, and leads us to discuss the suV)ject. 



