150 



PROF. ST. GEORGE MIYART ON 



drawn out at opposite poles and be irregularly constricted meri- 

 dionally and equatoriallj, and we get such a form as Botryocampe^ 

 one of a series of Polycystinian forms. 



Let this be open at one pole, and we get such forms as Eucyr- 

 tidium, Cyrtocalpis ohli^ua, and Cornutella (fig. 5). 



Let the margins of the open end be produced into spines, and 

 we get such forms as Lyclinocanium and Dictyopodium (fig. 6). 



Let one pole be greatly expanded and we have Eucecryphalus, 



Fig. 7. 



EiwecryphaUis Schultzei. (After Kolliker.) 



and finally we h&\e Lifharachnium tentorium^ which latter exhibits, 

 in the delicacy of its skeletal bars, a return towards the circum- 

 ferential network of Aulacantlia. 



rourthly, let the circumferential skeleton, as it is in Cyrtido- 

 sphwra^ be conceived as having its apertures greatly reduced and 

 its solid parts augmented in massiveness while they are reduced 

 in number, and we get such forms as Zygostephanus^^ Dicfyocha^j 

 and Acanthod€S7nia. 



But the circumferential skeleton may not only form a single 

 layer investing the capsule, for there may be two, three, or even 

 six more or less completely developed skeletal spheres concen- 

 trically investing the capsule, as in Arachnosphcera. These com- 

 plex concentric structures, however, are intimately connected 

 with and more or less dependent upon radiating skeletal elements, 

 80 that they will be best considered along with the radiating struc- 

 tures referred to. 



* L. c. plate xii. fig. 2. t L. c. plate xii. figs. 3 6. 



