TIM i in. .vii'iM i: .I:I;M \..\\ KK. .".1 



bio feature of ii b.-ing simple 



cubical, sometimes c\ lindric;.!, s< Hurt iiiu-s thread-. 



i-uds of which ordinarily reach tin- surface of tin- epithelium and arc 



'..:o\ided with cilia, whereas their i lie upon ' tutive 



lamella (>t lit /lamelle) of the body and I ited into one or 



.d filher Miiooth or t ran-\ etsely striped mu^de-ttbrilhe. Inasmuch as the 



librilhe of inimerou- oellfl lie parallel and close to 01. me II, t- 



\vhi<-h the <-l-:inges in the form of the bod, 



produced. / i '-literates loth //, '<iycrt can 



develop nnifi-le-ci'lls. 



When one turns to the Venues it is seen, in those groups in \vhi-h a : 

 cavity (jin eiiteroeu-1) is formed by an infolding of the inner germ-lay<r, that 

 the parietal wall of the body-cavity, or the parietal la: 'he middle 



germ-layer, has assumed the production of the entire musculature of the 

 trunk. Here also, for example in the Cluetognatha, etc., the epithelial cells 

 differentiate at their basal ends, which are directed toward the surface of 

 the body, a lamella of niuscle-librilliu, when . bound the 



l)cdy- cavity. Tim* from 1h<- loin-r to Uic Itiyhfr tin him I* tin- capability of 

 j>ro<lnchi;i iiiiitic'i-* /v. icith the prwjrcssirt' di >)',/;// f infin/i of the hotly, more and 

 more restricted to a limited special territory of the total cpltl 'merit 



of the body. 



This process has proceeded furthest in the Yeiu-brates, for in them the 

 musculature of the trunk is no longer furnished by the whole parietal lamella 

 of the middle germ-layer, but by only a small detached part of it, the primitive 

 nts. Consequently in Vertebrates the musculature spreads out from a 

 Miudl region where it originates, distributes itself first in the trunk, and then 

 from the latter grows out into the extremities. 



In the Vertebrates we recognised two different forms of voluntary musculature, 

 the muscle-layer (and the Mu>kelk;istchen derivable from it) and the primitive 

 bundle (Muskelprimitivbiindd). 1'arallels to this are found in the Inverte- 

 brates, both in Ccelenterates and in Worms. In Ccelenterates both forms are 

 derived from the primitive smoothly outspread muscle-lamella by the forma- 

 tion of folds, and are to be explained in the same way as the formation of those 

 folds which in epithelial lamellaj play such an important part in the origin of 

 the most various organs. When certain tracts of a muscle-lamella are called 

 upon to execute additional labor, this can be effected only by an increase 

 in the number of the librillse lying parallel to one anothar. But a greater 

 number of fibrilloe can be brought into a circumscribed territory only in one or 

 the other of two ways : either by tleir coming to lie in several layers one above 

 another, or if the more simple arrangement of lying side by side is to be 

 retained by the folding of the muscle-lamella. The folding exhibits two 

 modifications. Sometimes there are produced parallel daughter-lamrlhe placed 

 side by side and perpendicular t<> the mother-lamelhe ; sometimes the folded 

 lamellae become wholly detached from the parent -layer and converted into 

 muscle-cylinders, which imbed themselves in the underlying sustentative 

 lamella. 



With the conception here presented of the origin of the transversely striped 

 muscle-fibres of Vertebrates, it must be assumed as very probable that 

 subsequently an increase in their number will take place as a result of 

 constriction and detachment into two part.-, as \\as lirst maintained by 



WBISMANN, 



