Actiniae. 297 



parieto-basilar muscle on the sides facing the inter-mesenteric spaces, 

 in all except the directives, where the arrangement is reversed. 



Sphincter Muscle. — There is a strongly circumscribed endodermal 

 sphincter, which projects into the ccelenteron and is constricted off 

 from the body-wall to such an extent that in transverse section the 

 connection appears but a mere stalk (fig. 2). As here shown it is 

 oval in section, but doubtless it may vary in shape with the degree 

 of contraction. There is a single median supporting trunk of 

 mesogloeal connective tissue springing from the mesoglcea of the 

 body-wall, from which radiating lamelltTe arise covered with an 

 investing layer of muscle fibrillse (fig. 2, m.). 



Body-wall. — Sections of the body-wall show the mesoglcea com- 

 paratively thin, especially in the upper portion. There are, however, 

 strong circular endodermal muscles present, supported by mesogloeal 

 lamellae (fig. 4) which are often branched. These strong circular 

 muscles of the body-wall form one of the principal cliaracters dis- 

 tinguishing this species from the following one, where the corre- 

 sponding endodermal muscles are much feebler, supported by short, 

 simple, mesogloeal lamellee, and where, however, the mesoglcea itself 

 is thicker and firmer, thus compensating for the weaker muscles 

 (fig. 9). 



Brood Chambers.^ — Each adult female possesses peculiar brood 

 chambers completely separated from the ccelenteron and formed by 

 invaginations of the body-wall from a zone completely surrounding 

 the body, about one- third of the distance below the parapet (fig. 1). 

 Usually four embryos are present, and in later stages of development 

 they form conspicuous prominences symmetrically placed around the 

 column. In some instances the contained emljryos are so large 

 that in contraction the whole of the oral disc and tentacles of the 

 mother, as well as the upper third of the column itself, are with- 

 drawn so as to lie Ijelow the level of the ridge formed by the 

 contained embryos. 



Habitat. — Dredged from a gravelly bottom in 20-24 fathoms of 

 water, off Cape Adare, South Victoria Land. 



Urticina carlgreni. 



As one of the distinctive characters of this as well as the 

 preceding species is the presence of " brood chambers," I have 

 ventured to name this species after the Swedish naturalist, Oskar 

 Carlgren of Stockholm, whose valuable work on the Actinozoa has 



' For more detailed account, see p. 299. 



