ASEXUAL REPRODUCTION IN SAGARTIA 173 



by the fission plane and later resorbed; complete mesenteries 

 may be torn from the esophagus and persist as incomplete 

 mesenteries; incomplete mesenteries may adhere to the torn 

 edge of the esophagus and thus appear as complete mesenteries, 

 and one or more mesenteries , may be either wholly eliminated 

 by tearing during division or by this process combined with ab- 

 sorption during the early stages of regeneration. 



It should be emphasized that the irregularities just referred 

 to are distinctly exceptional. In general the plane of fission is 

 strictly vertical; and, considering the apparently mechanical 

 tearing of the tissues in fission, there is remarkably general 

 agreement between the mesenteries found in the separated 

 parts. 



Ordinarily an individual separates into two parts, which re- 

 generate for a considerable period before a second division super- 

 venes. Occasionally one finds instances, such as are represented 

 in table 5, of division resulting in the early formation of three or 

 more regenerating individuals. The case of no. 19 is typical. 

 It was a large diglyphic specim'en with twelve orange stripes and 

 giving no external evidence of a previous division. It was found 

 upon Fucus, where the slimy foothold may have operated to 

 prevent division. The presence of well-developed gonads, as 

 shown in the photographs of products of this division (figs. 27 

 to 32), may also be associated in some way with a delay in fission 

 under natural conditions. Upon being brought into the labora- 

 tory, like many other specimens, it promptly migrated on to the 

 glass surface of the container, and in about a week showed an 

 early stage of fission. One week later a division was completed, 

 resulting in one large and two smaller pieces. After three days 

 more the largest part had divided into two. There were then 

 four not very unequal pieces. Thirty-four days thereafter three 

 of the regenerating products of the division were killed, the 

 fourth having been lost. In no. 22 the interval between suc- 

 cessive fissions was eighteen days; in no. 17, twelve days; in 

 no. 18, two days. In nos. 20 and 21, as in the first division of 

 no. 19, the observations suggested simultaneous production of 

 three parts. The number of regenerating zones, however, as 



