CONTRIBUTIONS TO THE EMBRYOLOGY OF NEMERTBA. 441 
then be better understood why I must emphatically warn the 
reader against this tendency to give such considerable latitude 
to Huxley’s term of schizocel. This is all the more necessary 
as it is well known that in the Vertebrates and in certain 
higher Invertebrates an active splitting of the mesoblast may 
give rise to a true enterocel. If we adhere strictly to Huxley’s 
terminology we would here be obliged to apply the name 
schizoceel, and Huxley himself is naturally led to ask the 
question (1. c., p. 56) : “ whether the splitting of the mesoblast 
in the Vertebrate may not have a different meaning from the 
apparently similar process in the Arthropoda, Annelida, and 
Mollusca?” This question, which everyone will answer in 
the affirmative, so far as some of these groups are concerned, is 
the best proof that the name schizocel was not a fortunate one. 
The Hertwigs, instead of suppressing it, have considerably 
extended its significance in a way which I consider to be 
most unadvisable, and hence I propose to apply the name 
archicceel when it can be unquestionably demonstrated, as in 
Lineus, that the cavity has indeed been present from the very 
beginning, and to reserve the name of schizoccel for those 
cases when it can similarly be demonstrated that the perivis- 
ceral cavity originates by a process of active scission, and 
when this scission can in no way be looked upon as a derivation, 
either of archi- or of enterocel. Biitschli (‘ Morph.-Jahrb.,’ 
vol. vii, p. 474) has already attempted to bring about a com- 
parison between our archiccelom and the blood-vascular cavity 
of the Vertebrates. I need not point out that what we have 
found to exist in Nemertea appears to lend considerable support 
to this hypothesis. 
Before concluding our remarks about the origin of the 
different layers of the body wall we must not omit to notice 
the presence, in addition to the muscle-cells of the very cha- 
racteristic connective tissue that is found between the muscular 
fibres, between these and the cellular epiderm, and between 
these and the wall of the intestine. I need not point out that 
this connective tissue is eminently of mesoblastic origin, nor 
repeat that the space between the muscular body wall and the 
