ASTROSCLERA WILLEYANA, THE TYPE OF A NEW FAMILY OF SPONGES. 471 



thicker than the diameter of the ciliated chambers, so that the latter caiiuot be 

 seen actually in section. There is however another fact about this specimen which 

 may possibly explain the obscurity in the structure of its tissues. The canal system 

 contains in many parts hosts of minute deeply staining rod-like bodies (1 — ofi in 

 length), looking very like bacteria (Fig. 20, h.). They occur in scattered gi-oups or 

 apparently embedded in some clear homogeneous substance, in such masses, that they 

 appear to distend the canals. Three possibilities as to their nature have occurred 

 to me, namely, that they are bacteria, spermatozoa, or the remains of food. They 

 are not symbiotic bacteria, for they are absent from the two other specimens. The 

 cri.sp, evidently growing surface of this specimen, and the excellent preservation of 

 the eggs and embryos (those represented in Figs. 9 and 10 were contained in this 

 specimen), seems to put the view that the animal was undergoing decay, out of the 

 question. I do not think that the bodies are spermatozoa, for I have found no trace 

 of sperm morulae or any of the earlier stages of development of .spermatozoa. If they 

 are the remains of food it is remarkable that they should be found only in one 

 specimen, and I am moreover entirely at a loss to form a conjecture as to the 

 nature of the food which would leave such remains. 



Affinities. 



That the animal under consideration belongs to the Porifera seems clear from 

 the presence in the soft tissues of chambers provided with flagella and communicat- 

 ing with a system of canals which ultimately open to the exterior by pores. The 

 soft tissues are moreover supported by a skeleton composed of elements secreted by 

 cells scattered through the jelly. 



On the other hand that it is not a Coelenterate is shown by the absence of 

 polyps, mesenteries and thread-cells. 



There is at first sight some resemblance between a section of the skeleton of 

 Astrosclera and sections in certain planes of the skeleton of the Madreporarian Corals. 

 In these the fibres of the skeleton are disposed in fascicles and diverge from one 

 another about an axis which occupies the centre of the fascicle. A section which 

 cuts the fascicles transversely thus presents the appearance of fibres radially disposed 

 about a number of centres. Such a section is shown in Fig. 10 and other figures 

 of Miss Ogilvie's memoir " On the Microscopic and Systematic Study of the Madre- 

 porarian Types of Corals'." But, as Miss Ogilvie clearly shows, these systems of 

 radiating fibres are made up of lamellae successively deposited on the surface of the 

 skeleton, so that any particular fibre of a fascicle traverses many lamellae in its 

 course. We know from the work of von Koch, von Heider and others that the 

 skeleton is formed by a layer of cells, the calycoblasts, in contact with its surface. 

 It will be readily seen that the resemblance between these radiating systems of 

 fibres, and those formed within single cells of Astrosclera, can only be superficial. 



' Philosophical Transactions, vol. 187, B (18'JG). 



63—2 



