31(i DR. G. P, BIDDER : NOTES ON THE 



The suggestion is strong that ceroids, produced by the repeated division of 

 archseocytes, are in G. coriacea locomotor fertilizing elements which leave the 

 body and drift in the water, to enter eventually the oocyte of another sponge. 

 Whether they first develop a flagellum, and whether they co-exist with or are 

 replaced by the flagellate spermatozoa described (to the Linnean Society on 

 Dec. 11th, 1919) by Dr. Gatenby in Grantia, or the gregarine-like objects 

 which I have figured (PI. 24. figs. 4, 5, 6) emerging from [or entering — see 

 Postscript, p. 302] the cloacal wall of Sycon, it would as yet be futile to 

 discuss. 



[Sept. 20, 1920. — On the day that this MS. goes to press, I have a letter 

 from Mr. Julian Huxley, containing sketches of small cells which he has dis- 

 covered in the tissues of sponges. They have closely the appearance of 

 Plate 24. tig. 7, and judgment on the function of ceroids must be suspended 

 until his observations are available.] 



Note B. — Cessation of the Current (p. 301). 



When the collar-cells are completely covered by a lining of invading 

 porocytes (see 1892 b, fig. 2; 1897, p.' 487 ; 1900, fig. 42, F ; and 1908, 

 p. 326), there can be no current; and a motile spermatozoon could enter by 

 the osculum in those species (as Ascaltis cerebrum and A. reticulum) in which 

 the latter cannot close. Assuming that it is to the granules of the porocytes 

 that the Clathrinidae owe their characteristic scent, the spermatozoa, after the 

 osculum is passed, will enter a highly odoriferous chamber, to the porocyte- 

 lined walls of which they will be strongly attracted. 



The current may also be completely stopped by the clogging of the pylo- 

 cytes and, in Heterocoel sponges, by the choking of the afferent canals. I 

 have found this happen in ten minutes to Leucandra aspera fed with indigo, 

 and in half-an-hour, when fed with Indian ink, the current was very much 

 diminished ; sea-water, milk-white with starch, stopped the current in two 

 minutes. In nature similar cessation must be at times caused by unusual 

 turbidity of the water.* 



Outside these two cases, it may be assumed on purely general grounds that 

 pathological conditions may kill or paralyse the collar-cells, while leaving the 

 ova still susceptible of successful fertilisation. Thus, Annandale (1907, 



* That such cessation is not due in Calcaronea to reflex closure of the pores, as stated by 

 Lendenfeld (cf. 1895, p. 33), is proved by the fact that sections show the pylocytes widely 

 open and choked with starch grains (see ante, p. 308, fig. F). Parker's experiments 

 (1910 6) on Stylotetta have led him to the same conclusion, and to a similar disbelief in 

 Lendenfeld's assertions. 



The form of a pylocyte, viewed from one of the surfaces, is strongly suggestive of a 

 sphincter, but I believe this suggestion to be delusive. A pylocyte is a perforated cell whose 

 differentiation is to make intracellular communication between one cavity and another ; it 

 is comparable to a cell in the channel of anephridium, and not to a muscle-cell ; it is a radial 

 cell perforated radially, not a tangential fusiform cell whose ends are united, and the forces 

 exerted by the cell oppose those of surface-tension which would obliterate the lumen. 



