FISSION IN NEMBERTINES. 25 
occurrence of some kind of solvent action—the fibrils may be 
“eaten through,” as it were; but I know of no means of 
deciding the matter. 
The process, whatever its details, seems to be different from 
that which occurs in Planarians, such as Microstoma, which 
reproduce asexually by fission. 
In his account of the process, van Wagner (‘ Zool. Jahr- 
buch,’ iv, 1891) expressly states that there are no nuclei in 
the “ septa,’ which make their appearance along the lines of 
the future separation of the individual into zooids. Each septum 
is represented in v. Wagner’s illustrations as being of some 
homogeneous tissue, passing from the subepidermic muscles 
to the muscularis of the intestine. He gives no details as to 
how the “ parenchyma” separates, which bear any resemblance 
to those detailed in the process of rupture of the muscles seen 
inthis Nemertine. Further, there is a great deal of ‘‘ regene- 
ration ”’—i.e. formation of new brain, new pharynx, &c.—in 
Microstoma before separation takes place. Of this there is 
no trace in Carinella. I need not enter here upon the vexed 
question as to the distinction between “ division” and “ gem- 
mation.” In Carinella there seems no doubt that the process 
is “ division.” 
A second part of the problem relates to the meaning of the 
whole process in regard to the life of the animal. It is 
generally assumed, and apparently rightly assumed, that the 
process of rupture will be of advantage to the Nemertine, in 
that each of the pieces thus formed will be able to give rise to 
gonads, as M‘Intosh observed; in most cases, however, there 
does not seem to be any direct relation between rupture and 
genital maturity. But in the present instance there is such a 
relation, for in both the specimens the genital elements are 
only present in the hinder part of the worm, which 
is being separated off from the rest. 
In the specimen I (fig. 1), which is a female, the gonads are 
present in each of the four “segments,” and no trace of ova 
exists in front of the line B, while behind the line A the ova are 
larger and more numerous than in front of it. 
