156 ART. T. 1. IJIMA : HEXACTINELLIDA, IV. 



the dermal membrane and the trabeculse, strengthen me in the 

 belief that the two parts just mentioned are genetically and 

 fundamentally one and the same structure, whatever differences 

 apparently exist between them being due to the circumstances of 

 their respective situations (see Contril). I., pp. 122, 147). 



The gastral membrane is of much the same appearance as 

 the dermal. 



The thesocytes of the species are of a characteristic appearance. 

 They may occur in the dermal and gastral membranes as well as 

 on trabecuhe in all parts of the sponge-wall, but seem to be most 

 abundant in the subdermal region. They are show^n in numbers 

 in PI. XL, fig. 18, in wdiich they appear as morula-like masses 

 consisting of numerous small spherules. The quantities in which 

 they occur are subject to variation according to individuals ; but 

 they seem to be present all the year round, since I have observed 

 them in specimens preserved in the months of April, July, 

 August and December. 



The thesocytes are spherical, ovoid or somewhat irregular in 

 shape and may be more or less flattened when situated on or 

 against a membranously expanded trabecula. They measure 8- 

 20 /^ across. A fine cell-limit and the nucleus are only excep- 

 tionally distinguishable ; the former can be perceived only when 

 the spherules contained in it are not developed in too excessive 

 numbers, while the latter is generally concealed among the 

 spherules. 



The spherules, which measure 1.7-2.5/^ are refractive and 

 homogeneous, appearing yellowish in the unstained state. Their 

 reactions towards different stains have already been noticed on p. 

 178 (foot-note) of my Contribution I. and therefore need not be 



