44 ART. 1. — î. IJIMA : HEXACTINELLIDA, III. 



way of interpreting the source of tlie larva, the reader is referred 

 to my enunciations in my Contribution I., pp. 185-190. 



By the time the larve has gro\Yn to a size of 60-70 1'- 

 diameter, the first spicules make their appearance (PI. III., fig. 

 24). These are minute and delicate-rayed oxystauractins, — not 

 liexactins, contrary to what might be expected on a priori 

 grounds. It does not necessarily follow from this that stauractins 

 represent the most primitive form of Hexactinellid spicules. I 

 simply consider that the stauractinic form of the spicules develop- 

 ing first in the ontogeny is due to the suppression of one of the 

 three primitively present axes, in adaptation to a cei'tain secondary 

 condition of the larva — assumably to circumstances of the space 

 in which the spicules develop themselves, as seems to hold true 

 in a general way of all triaxonic spicules with a reduced number 

 of rays. A close investigation of the central cross of the axial 

 filaments — which however can not be undertaken with the objects 

 in hand — will presumably reveal an abortive third filament re- 

 presenting the suppressed axis. 



The said embryonal oxystauractins are situated in the periphery 

 of the central cell-mass, with the plane of the four rays disposed 

 paratangentially to the surface of the larva ; they lie not in 

 direct contact with the external epithelium but well separated 

 from its internal limit by a few cells of the internal mass. To 

 give a connected account of what I have seen in several larv{:e, 

 the oxystauractins are at first scattered singly ; they are by no 

 means numerous in number and show no definite rule as to the 

 manner of relative distribution, except in that they always occur 

 in a single layer. They grow in size, apparently without increas- 

 ing in number ; all seem to have taken origin nearly simultaneously 

 and are therefore of aj)})roximately the same size. They soon 



