MATERIALS FOR A MONOGRAPH OF THE ASCONS. 523 



the long kind by division of the nucleus after the actinoblast 

 has retreated from the base of the ray. Ou the other hand, in 

 fig. 33 the spicule ray is shown to be in its infancy from the 

 way in which the actinoblast extends down to the base, and 

 the presence of two nuclei gives every promise of a future 

 great development in size of the spicule ray. 



The facts both in cerebrum and reticulum point to an 

 incipient differentiation of the quadriradiates into two classes, 

 already quite distinct in typical examples, but as yet connected 

 by transitions. In reticulum, at least, the spicules of one 

 class can probably become actually converted into spicules of 

 the other class. In view of the manv instances amongst 

 Ascons and Calcarea generally of the spicules of a particular 

 kind — triradiates, quadriradiates, or monaxons — being differ- 

 entiated into two classes as a specific character, these facts are 

 not without interest. 



There remains one fact to mention with regard to the 

 gastral actinoblasts, and that is the frequent occurrence in 

 them of rod-shaped or needle-like bodies of crystalline appear- 

 ance (PI. 39, fig. 18, PL 40, fig. 30, and PL 41, fig. 41, x). I 

 am unable to state what may be their nature or significance. 

 That shown in fig. 41 was most distinct, and is interesting as 

 occurring in a decalcified specimen. 



To sum up the facts observed with reference to the quadri- 

 radiate spicules, the fourth or gastral ray is an adven- 

 titious element superadded to the triradiate system, 

 and secreted by a mother-cell which is derived from 

 a porocyte. The nucleus of the secreting cell may 

 remain single, or divide into two or into four uuclei; 

 but in all cases the cell itself remains undivided, 

 forming a plasmodium-like investment to the spicule, 

 or at least to its terminal portion. 



(c) Some Observations on the Formation of the 

 Monaxon Spicules. — In a former paper (1896) I described 

 the formation of the monaxon spicules in young stages of 

 Leucosolenia variabilis, and showed that they originated 

 each in a single cell of the flat epithelium. I studied at 



