n CNIDARIA MUSCULATURE 87 



extended. In the medusoid swimming bells of the Siphonophora, just 

 as in the Craspedote Medusce, a layer of striated ectodermal circular 

 muscle fibres is developed in the subumbrella and in the velum. 



We find the two systems of muscles in the Medusce also, the longi- 

 tudinal and the circular, though the latter is here ectodermal. The 

 longitudinal muscle fibres are generally smooth, the circular muscle 

 fibres usually striated. The muscle fibres are mostly processes from 

 the epithelial muscle cells ; but there are also muscle bands and strands 

 which quite detach themselves from the epithelium, and run in the 

 gelatinous connective tissue as independent mesodermal muscles. The 

 exumbrella is poor in muscles, sometimes even having none at all. In 

 the remainder of the body, the longitudinal as well as the circular 

 musculature falls into three systems : (1) into a system spreading over 

 the gastric or oral peduncle ; (2) a system spreading over the sub- 

 umbrella from the base of the oral peduncle to the margin of the disc ; 

 (3) a system developed at the margin of the disc itself (musculature 

 of the tentacles, the velum, and the velarium). In correspondence 

 with this, the three systems of the longitudinal musculature are as 

 follows : 



A. The longitudinal musculature of the oral peduncle (serving for 

 its contraction and retraction). 



B. The radial muscles, which run radially from the base of the oral 

 peduncle towards the margin of the disc. 



C. The longitudinal muscles of the tentacles and marginal lobes. 



The three systems of the circular musculature are as follows : 



A. The circular musculature of the oral peduncle. 



B. The circular musculature of the subumbrella, developed in the 

 Craspedota over its whole extent, but in the Acraspeda generally form- 

 ing a narrower but very strong peripheral muscle (Fig. 67, m, p. 77) 

 near the circumference of the subumbrella. 



C. The strong circular musculature of the Craspedote velum, and 

 the circular musculature of the Acraspede marginal lobes and velarium. 



In Scyphostoma and many lower Acraspeda, especially in attached 

 forms, e.g. Lucernaria, there are 4 (seldom 8) interradial septal 

 or funnel muscles (peduncular muscles) which, starting from near the 

 oral disc, or that portion of the subumbrella which borders on the oral 

 peduncle, run through the body as far as the aboral attached apex of 

 the exumbrella. They lie in the 4 septa which separate the 4 

 gastric pouches on their axial sides, and then proceed upwards in the 

 prolongations of the septa, i.e. in the 4 gastric ridges or ta3nioles. 

 According to recent research, they arise in the ectodermal cells of a 

 solid prolongation of the 4 interradial septal funnels, which grow 

 towards the aboral pole ; we shall speak of these septal funnels later. 



The endodermal musculature of the Corals, in contradistinction to 

 that of all the other Cnidaria, is at least as much if not more developed 



