ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 747 



spicules, while the amphidiscs arise in almost spherical and only 

 laterally compressed silicoblasts. The central filament is rich in water. 

 As to the origin of the silex we know nothing definitely. The activity 

 of the mother-cells appears to be periodic, for it sometimes secretes 

 spiculin, and then again silex. The cell-contents of the silicoblast are 

 soluble and give rise to the central filament ; around this silica is 

 deposited, and so the axial cylinder is formed ; layers of silica with their 

 membrane succeed one another until the mother-cell is used up. The 

 spongoblasts are cells which differ essentially from the silicoblasts, 

 and in Spongilla are often remarkable for their large size ; in it and 

 Desmacidon they have the same form and position. 



The water, which passes by numerous pores into the sponge, first 

 passes into the meshes of the subdermal network, whence it is distributed 

 to numerous fine canaliculi, to pass to the flagellated chambers which 

 are scattered throughout the whole of the parenchyma. Other canaliculi 

 surround them and carry off the water directly to the elierent orifices. 

 D. Bosci appears to belong to Vosmaer's third type, for the region of 

 collar-cells opens directly into wide canals, and then again into wider 

 vessels, or cloacal cavities which open to the exterior. 



It is possible that the new sponge is bisexual, but the evidence as to 

 the spermatozoa is incomplete. Ova are developed in great numbers and 

 are found in all parts of the tissue ; they are rapidly aud easily stained, 

 and can also be recognized by their considerable size from the cells 

 among which they lie. The nucleus and nucleolus are well marked, but 

 the finely granular protoplasm is not bounded by any membrane ; indeed, 

 they vary in form, and are certainly amoeboid. Their further develop- 

 ment is commenced within the sponge ; when four blastomeres are formed 

 a follicle becomes developed, which has the form of an extremely fine 

 membranous investment, and is found in all further stages of develop- 

 ment observed within the sponge as a closed capsule. 



The author concludes with some observations on the systematic 

 characters of the genus Desmacidon. 



' Challeng^er ' Hexactinellida.* — Apart from the systematic portion 

 of Prof. F. E. Schulze's monogrfiph on Hexactinellida included in the 

 reports of the ' Challenger ' expedition, the results of most value are to be 

 found in the discussion of the general, structure of the soft and hard parts, 

 and of the general system of the group. Of the ninety forms ollected 

 by the ' Challenger,' fifty-nine were new, and in addition to these nine 

 new species from other sources are described. The geographical and 

 bathymetrical distribution of the Hexactinellida are discussed at lenofth, 

 and furnish valuable results. From the nature of the case, but few histo- 

 logical results were forthcoming. Thus Schulze was unable to demon- 

 strate the collars or flagella of the ciliated chambers, or the contours of 

 the flat epithelial cells. The only chapter in regard to which serious 

 difterence of opinion can arise is of course that which deals with the 

 phylogeny. The Hexactinellida are all derived from a common stem. 

 From this the Hyalonematidae early diverged. The other branch in- 

 cludes the Uncinataria (Dictyonina minus Mseandrospongias), an offshoot 

 for the Euplectellidee, Eossellidse, and Asconematidse, and the M^eandro- 

 spongise. 



* Keports of the Voyage of H.M.S. 'Challenger,' Zoology, xxi. (18S8) 513 pp. 

 (105 pis.). 



