APPENDIX — SPONGES OF THE "ARGO" CRTTISE. 217 



irregular arrangement of the spicules. Two germ-layers 

 can easily be made out in it, but there is no clue as to the 

 third one. An embryo very similar to that of EspereUa 

 sordida has recently been figured by Lendenfeld* for 

 JPlwrospongia chaliniformis. It also resembles it in the 

 regular arrangement of the spicules, but differs from it in 

 its cubical ectoderm. Lendenfeld calls the central portion 

 of the embryo " endodermal mass," although in contains 

 spicules and shows generally no great similarity to the 

 endoderm of the adult sponge. It is certain that this 

 embryonic stage has not yet been explained satisfactorily 

 and that additional work is necessary. 



Iophon lujndmani, Bowerbank. 



The specimen which I refer to above species, does not 

 differ from the type described by Bowerbank except very 

 slightly in the relative thickness of the megascleres, and 

 I think it safe to include the two forms under a common 

 name. The only specimen obtained is a minute fragment 

 of brownish colour, about 3 mm. in diameter, which was 

 attached to the piece of rock dredged off Arran Islands. 

 The megascleres are of two kinds, viz : — Strongyla, 0'18 

 by O003 mm. Although slender, they are not so slender 

 as those figured by Bowerbank.-"- Secondly : spined styli, 

 varying greatly in size, from O088 by 0"0035 mm. to 0'28 

 by 0' 006 mm. They are more slender than those figured 

 by Bowerbank. The microscleres are also of two forms, 

 viz : — bipocilli which are so characteristic of the genus, 

 0"0087 mm. in length, and palmate anisochelse, 0*02 mm. 

 in length. 



Bowerbank described four species of this genus, Hali- 

 chondria pattersoni, H. hyndmani, H. scandens and H. 



* R. v. Lendenfeld, A Monograph of the Horny Sponges, pi. xli., fig. 2. 

 t Bowerbank, loc. eit., vol. iii, pi. xlvi, fig. 2. 



