On the Ilccactnie Spicule of Htxactindlida. .OOj 



specimens from the Kentei and Ussuii, representing Scliienck'd 

 " Lagomys hifperboreus, var. cinereo-fusca," are witli'iut dates, 

 but tlic present series enables mc to determine then) with 

 contidencc as being respectively summer and winter examples 

 of one form. 



'J'liis animal would appear to be not more than sub.speci- 

 fically di6tin;;;uisliable from cinereo-ftisca, and as Schrenck 

 considered that a variety of li'/perborea I do the aanio for 

 the present form ; but the intergradation with the Tschuktschi 

 Pika may hereafter prove to be broken, ami the Amur and 

 ]\Iantchurian furms to be worthy of specific separation from 

 the more northern species. 



Ij. Capreolus hedj'ordi^ Thos. 

 ? and two young. Khingan Mts. 



LX 1 1 1. — On the Regidar Hexactine Spicule of Uexactinellida. 

 By R. KiRKPATincK. 



The regular hexactine spicule characteristic of Ilexictineliid 

 sponges has three axes crossing at right angles through a 

 common centre and corresponding with the axes of the regul.ir 

 crystalline system; but the silica of which the spicule is 

 composed is isotropic and amoiphous. What is the meaning 

 of tilt' form of the regular hexactin* ? Is it due to ])urely 

 organic causes, or is its shape influenced by its mineral 

 characters; or do both of these factors contribute ? Further, 

 if its form is due to biological causes, how have they fashionoil 

 the regular hexactine shape? Before attempting to suggest 

 an answer to these questions I will refer to theories already 

 put forward by Schulze and JMinchin. 



The typical Hcxactinellid sponge is a cup-shaped lamina 

 ■with a central layer of thimble-shaped flagellated chambers 

 suspended between an outer dermal and an inner gastral 

 layer of delicate netwoik. Schulze f was of opinion tliat the 

 regular hexactine s|iicule came into existence because it was 

 adapted to support the tliimble-shaped flagellated chambers. 



Minchin \ has stated his belief that the S|)icules arose before 

 tlie flagellated chambers were formed, that the stauractin 

 preceded the hexactin, and that the symmetry of these two 



• I use the term actiue as an adjective, and nctin as a substautive. 

 t ' Challong-er' IJeport. Ilexactinellida, \*^fil , p. 604. 

 X " A Speculaliou on tlie l'hyloj:euy of the ilexactinellid Sponges," 

 Zool. Anzei;^«T, UK).'), xxviii. p. 4,i9. 



