1892.] and Spongoblasts in one of the Keratosa. 137 



cuticle of a large number of such cells poured out (in this sponge) 

 around an intrusive foreign object. 



I referred (loc. cit.), as if well known, to the "hexagonal markings 

 of the horny fibre." I cannot, however, find any mention of them in 

 the literature of the subject, except by Polejaeff (' Keratosa,' p. 70). 

 As he there describes them as an exceptional structure, and as I find 

 them not nearly so easily to be made out in Gacospongia as in Aplysilla* 

 it is possible that they have hitherto escaped notice. They are fine 

 black lines, having the exact appearance of the network on the surface 

 of an epithelium, and I regard it as beyond doubt that they mark the 

 lines of contact between the expanded secreting ends of the spongo- 

 blasts. 



An interpretation of the histology of Ascetta clathrus, differing con- 

 siderably from mine, appears in the ' Zoologischer Anzeiger,' No. 391, 

 for this year. It would be under- valuing Mr. Minchin's researches 

 to attempt serious comment on them until I have had the opportunity 

 of re-examining my preparations in the light of his conclusions. How 

 far his theory of a contractile ectoderm may be applicable to such an 

 extreme form as that found in Cacospongia is a matter demanding 

 the gravest consideration.f 



The newly-established points on which we find ourselves in agree- 

 ment are : (1) The pores of Ascetta clatJirus are composed each of a 

 single, nucleate, perforated cell ; these cells have by various authors 

 been mistaken for mesoderm cells. (2) The ectoderm is, in life, in a 

 large part composed of cells which are roughly "|~" 8na P e( i i n section, 

 the nucleus lying at the base of the stalk of the "[" 



On a minor and not very novel point we are in agreement as to 

 there being, at any rate commonly, at least one vacuole in the distal 

 part of the collar cell, frequently containing shapeless particles. As 

 to our differences, I am undecided whether Minchin's mesodermal 

 " potato-shaped wandering cell, of greenish-yellow colour," is what I 



* The determination of these sponges must be taken with reserve ; the fear of 

 angels to tread among Keratose genera makes me postpone as far as possible my 

 first step ! Both species are found in the Bay of Naples. The " Cacofpongia " is 

 firm, massive, somewhat incrusting, conulate, with conspicuous antler- like primary 

 fibres, heavily cored with foreign bodies ; the delicate secondaries show in their 

 axis fine black spots; skin black, pulp white. "Aplysilla" corresponds in general 

 description with Schmidt's Aplysina aerophoba, the yellow crust bearing vertical 

 twig-like prominences, mostly supported by a single fibre ; under unhealthy condi- 

 tions, the living part of the prominences contracts up the fibre like a bud. In the 

 axis of the fibre at least in one specimen I have observed a row of indubitable 

 cells, amoeboid in appearance j presumably they are what Lendenfeld has described 

 as " spongoklasts." 



f It is obvious that the presence, as in this sponge, of a fairly strong cuticle, even 

 though it be " elastic " (Schulze), renders it much more difficult to assume that the 

 form of the cells has been produced by their contraction. (July 15. The continuity 

 with the spongoblasts greatly increases the difficulty of such an hypothesis.) 



