I 



24 THE VOYAGE OF H.M.S. CHALLENGER. 



such as are found in the red clay, in the other (fig. 5). Thus it appears that the three 

 principal abyssal deposits — Globigerina ooze, Radiol arian ooze, and red clay — supply 

 accidentally the materials of which the pseudo-skeleton in these Ammoconidse, as well 

 as in the following families of Deep-sea Keratosa, is composed. 



Soft Parts. — Whilst the main mass of the tubular body in all the Ammoconidse is 

 composed of xenophya, or of foreign bodies received from the ooze of the sea-bottom, 

 the true organic tissue of the sponge itself is represented only by the thin delicate 

 membrane which connects and encloses the xenophya. The nature of this membrane is 

 best recognised in those species in which the calcareous matter may be removed by 

 treatment with acids. The delicate residue is formed by a thin, transparent, or somewhat 

 granular membrane, which closer examination proves to be a soft maltha, or mesodermal 

 ground-mass, in which two kinds of cells are enclosed : small, roundish, fusiform or stellate, 

 connective cells, and larger amoeboid wandering cells. Besides, in one species (Ammo- 

 lynthus prototypus, PI. VIII. fig. 1) larger amoeboid cells could be recognised, possessing 

 a large clear spherical nucleus with a small dark nucleolus (figs. IB, lC, e, v). These 

 cannot be distinguished from the common naked eggs of sponges ; stages of segmentation, 

 however, and larvae (Gastrulse) were not observed in these Ammoconidse. The same 

 must be said of the (hypothetical) exodermal pavement-epithelium, whereas remnants 

 , of the entodermal flagellated epithelium were recognisable on the inside of some tubular 

 Ammoconidse (PI. VIII. figs. IB, 10, n). 



Ammoconidse and Rhabdamminidse. — The peculiar deep-sea organisms here 

 described as Ammoconidse exhibit a striking resemblance to certain Rhabdamminidse, 

 described as Foraminifera Astrorhizida in Henry B. Brady's Report. 1 We find a striking 

 similarity between Ammolynthus and Rhabdammina, between Ammosolenia and 

 Rhizammina, between Ammoconia and Sagenella. Brady thus characterises the family 

 Astrorhizidse : — " Test invariably composite, usually of large size and monothalamous ; 

 often branched or radiate, sometimes segmented by constriction of the walls, but 

 seldom or never truly septate; polythalamous forms never symmetrical." 2 The 

 subfamily Rhabdamminidse is characterised as follows : — " Test composed of firmly 

 cemented sand-grains, often with sponge-spicules intermixed, tubular, straight, radiate, 

 branched or irregular, free or adherent, with one, two, or more apertures, rarely 

 segmented." 3 For further comparison see the careful description of Brady. 



Judging as to the nature and affinities of these gigantic deep-sea Rhizopods (the 

 majority of which have been recently described), it must not be forgotten that we know 

 very little more than the external form and the structure of their arenaceous shell. 

 The internal organisation, and even the organic contents, of the shells are almost 

 unknown, except in a few cases. On the other hand, the general form of the numerous 



1 Zool. Chall. Exp., pt. xxii. pp. 63, 227, pis. xix.-xxviii. 



2 Loc. cit, p. 63. 3 Loc. cit., p. 64. 



