SPONGES. KALLMANN. j^j 



This introduces an interesting point in connection with the 

 megascleres, viz., their versatiUty in respect to the different 

 parts they play in different genera in the conformation of the 

 skeleton ; and it also raises the question as to the nature of the 

 criteria at our disposal for determining, in a given species, to 

 ^vhich category — principal, accessory or auxiliary — the megas- 

 cleres of each kind belong. According to my interpretation, 

 if we take into account only the situation of the megascleres, 

 the following types of skeleton are, amongst others, dis- 

 tinguishable : — 



I- — The spicules of the fibres are "basicals" of one or two 

 kinds; the "auxiliaries," if (as is almost invariabh- the case) 

 present, occur interstitially' and dermally. 



{a) The "basicals" are of two kinds, both of which occur 

 in connection with the fibres. 



(i.) The fibres are cored by "principals" and echinated 

 by "accessories." Normal "Ectvoninae. " 



(ii.) Both kinds of "basicals" are longitudinally dis- 

 posed in the fibres. "r/af/zna" chartacca {vide 

 remarks on ClatJiria) : Heteroclathna. 



(h) The "basicals" are scarcely or not at all differentiated 

 into two groups, and echmating spicules, if present, are not 

 distinguishable in form from the directive spicules ; or either 

 the one kind or the other of the "principal" and "acces- 

 sory" groups has been lost by atrophy. 



(iii.) The "basicals" are imperfectly differentiated. 

 Stylostichon. 



(iv.) "Accessories" are absent. Normal "Dendori- 

 cince," Ophlitaspongia, EchinocJathria. 



(v). "Principals" are absent. ''Clatlnia'' mollis,'^ 

 Paraniyxilhi iiijrcquois."^ 



II. — The spicules composing the fibres comprise both "basi- 

 cals" and "auxiliaries;" the latter, which are situated axially 

 in the fibres also occur interstitially or dermally. 



(vi.) Principal and accessory spicules are well distin- 

 guished, and both kinds are associated with the 

 fibres. "'Echinodictyuni'' ridJeyi (p. 151). 



1 Kirkpatrick— Marine Investigations in South Africa, ii., 1904, p. 249. 



2 Carter— Ann. Mag. Nat. Hist. (5), vii., 1881, p. 369: Dendy— Keport Pearl 



Oyster Fisheries, Gulf of Manaar, iii., 1905, p. 233. 



