REPORT ON THE DEEP-SEA KERATOSA. 15 



(I.) The common ground-mass or maltha ; (II.) the cells scattered in the maltha ; and 

 (III.) the various skeletal productions. The cells scattered in the maltha belong in our 

 Keratosa to three different groups, viz., (l) malthocytes or collencytes (usual connective 

 cells) ; (2) amcebocytes (amoeboid wandering cells) ; and (3) gonocytes, or sexual cells 

 (eggs and sperm). 



Maltha. — The common ground-mass of the connective tissue, which we call shortly 

 maltha, is usually described as ground-mass, matrix, intercellular substance, mesoglcea, 

 collenchyma, &c. It is secreted by the connective cells of the mesoderm, which are 

 derived originally from the primary exoderm cells. Those spongiologists who have 

 especially examined the Keratosa (F. E. Schulze, Lendenfeld, Polejaeff, and others) 

 distinguish in this group two different main forms of the maltha ; it is clear and trans- 

 parent in the Macrocameras (Spongelidse and Darwinellida;), and granular and opaque 

 in the Microcamerae (Euspongkke and Aplysinidad). All the Keratosa of the deep sea (as 

 far as the maltha is well preserved) seem to agree in this respect with the Spongelidse ; 

 their mesodermal ground-mass is clear and transparent, in most species soft, scantily 

 developed, and not voluminous. 



Malthocytes or Collencytes. — The common cells of the connective tissue, which produce 

 the maltha or matrix of it by secretion, are not very abundant in the Deep-sea Keratosa, 

 and may be easily overlooked in the examination of the scanty maltha, owing to the 

 predominant masses of xenophya filling up the latter. The best objects for their 

 examination (as for that of the maltha in general) are those Keratosa in which the 

 xenophya are calcareous, derived from Globigerina ooze. Having dissolved the calcareous 

 matter by dilute acids, there remains a soft and transparent maltha, in which the small 

 malthocytes are scattered irregularly. Their form is usually stellate or spindle-shaped, 

 with a small granular ovate nucleus, a little protoplasm, and a few short pointed 

 apophyses. 



Amabocytes. — The remarkable amoeboid wandering cells, which seem to possess an 

 important physiological function in all sponges, are also found in our Deep-sea Keratosa. 

 They are scattered in the maltha in far less numbers than the malthocytes, and may 

 easily be distinguished from them by the larger size of the protoplasmic cell-body as 

 well as of the clear vesicular nucleus. The more voluminous protoplasm usually encloses 

 a variable mass of dark, highly refracting, and intensely staining granules, and often 

 these enter in the lappet-like processes, or lobopodia of the cell, as in the similar common 

 Amcebse. The Amcebocytes of the sponges are comparable to the Leucocytes of the higher 

 Metazoa, and are probably derived from the original, not differentiated, exoderm cells. 

 Their functions are probably multifarious, referring mainly to the nutrition of the sponge. 

 They may be vehicles of food and of reserve nutriments. But in the Stannomidse they 

 may also produce the peculiar spongin-fibrillas of this family, comparable to odonto- 

 blasts which produce dentin fibrillse. 



