. The Cambridge natural history. Zoology. 172 EORIFERA CHAP. pointed at both ends it receives the special name oxea. The lamination of the spicule is rendered much more distinct by heat- ing or treatment with caustic potash.''. Fio. 66. Cut end of a length of a siliceous spicule from Hyalonema sieboldii, with the lamellar structure revealed by solution. x 104. (After Sollas.) The archaeocytes are rounded amoeboid cells early set apart in the larva; they are practically undifferentiated blastomeres. Some of them become reproductive elements, and thus afford a good instance of " continuity
. The Cambridge natural history. Zoology. 172 EORIFERA CHAP. pointed at both ends it receives the special name oxea. The lamination of the spicule is rendered much more distinct by heat- ing or treatment with caustic potash.''. Fio. 66. Cut end of a length of a siliceous spicule from Hyalonema sieboldii, with the lamellar structure revealed by solution. x 104. (After Sollas.) The archaeocytes are rounded amoeboid cells early set apart in the larva; they are practically undifferentiated blastomeres. Some of them become reproductive elements, and thus afford a good instance of " continuity of germ plasm," others probably perform excretory functions.^ The reproductive elements are ova and spermatozoa, and are to be found in all stages in the dermal jelly. Dendy states that the eggs are fertilised in the inhalant canals, to which position they migrate by amoeboid movements, and there become suspended by a peduncle. The larva has unfortunately not been described, but as the course of development among the near relatives of H. panicea is known to be fairly constant, it will be con- venient to give a description of a " Hali- chondrine type" of larva based on Maas' account of the development of Gellius varius? jd X The free-swimming larvae escape by the Fig. 67.—Free-swimming osculum ; they are minute oval bodies moving f:^l^fZZr'l rapidly by means of a covering of cilia. Outer epithelium; pi, The greater part of the body is a dazzling ^i,r"(Afte^'Mal:T ^hite, while the hinder pole is of a_ brown violet colour. This coloured patch is non- ciliate, the general covering of cilia ending at its edge in a ring of cilia twice the length of the others. Forward move- 1 Sollas, Ann. Mag. Nat. Hist. (4) xx. 1877, p. 2S5 ;.Butsohli, Zcilschr. f. wiss. Zool. xix. 1901, p. 236. ^ Minchin, "Sponges" in Treatise on Zoology, edited by E. Ray Lankester, p. 87. See also Bidder, Proc. Roy. Soc. li. 1892, p. 474. ' Zool. Jalirh. Anat. vii. Please not
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