ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 967 



tlie nucleus is occupied by a nucleolus which stains very easily ; the rest 

 of the nuclear cavity is clear, and is often, especially in the later stages 

 of development, traversed by a few chromatin filaments, while small 

 spherules of chromatin are deposited at the periphery. The ova exhibit 

 great variability in their position relatively to the other cells of the 

 parenchyma ; the follicle first arises owing to the continuous growth of 

 the egg-cell, the pressure thus caused producing an approximation of 

 adjacent cells. The older follicles are more like one another than the 

 younger. Those of the young egg consist of cells varying in number 

 and form. The history of the follicle is described at some length. 



When the egg-cell has attained its full size the changes begin in it 

 which have been associated with the " maturation of the ovum " ; the 

 nucleus wanders towards the surface to eliminate the directive corpuscles ; 

 it is to be noted, however, that the characteristic spindle-figures have 

 not yet been observed. The whole process of segmentation is never the 

 so-called indirect, but always a modified form of direct nuclear division. 



The cells of Spongilla which give rise to the spermatozoa have a 

 rather finely granular protoplasm and a proportionately large nucleus ; 

 the latter consists of a thick network of chromatin with numerous 

 nucleoli which appear to lie at the nodal points of the network. Two 

 nuclei next appear, one of which is as rich in chromatin as the first 

 nucleus, while the second, which is more superficial in position, is very 

 much poorer in chromatin and somewhat smaller. Its j)rotoplasm was 

 sometimes found to be separated by a fine line from that of the inner 

 nucleus. Later on this separation becomes more distinct, and it is seen 

 that a delicate layer of protoplasm with a double contour incloses a 

 number of cells which are to be regarded as the products of division of 

 the internal nucleus and of its protoplasmic investment. The ripe 

 spermatozoa have a spherical head and a small tail which is set in the 

 direction of the long axis of the head. 



The male elements of Spongilla are so small as to come almost to 

 the limits of vision possible with our Microscopes. The author compares 

 and discusses his results with those of observers of the spermatogenesis 

 of other species of Sponges. 



Remarkable Spicules from the Oamaru Deposit* — Mr. B. W. 

 Priest has found in some material from the deposit from Oamaru, New- 

 Zealand, two spicules, one an acerate, the other a trifid, in which the 

 enlarged axial cavities have a spiral, vermiform body lying within them, 

 and perfectly siliceous. The author cannot " quite grasp the idea " of a 

 vegetable organism penetrating a siliceous substance, " excepting that 

 some chemical caustic action is set up." 



Protozoa. 



Phylogeny of Protozoa.f— Prof. O. Biitschli has published an in- 

 teresting introduction to his first volume on the Protozoa. After an 

 important historical account, he gives a phylogenetic table (see next 

 page), which exhibits his own views on the classification of the group. 



The root of all the unicellular forms must be sought for not in 

 amoeboid organisms, but in those which stand between the Sarcodina 

 and the Mastigophora ; they are, perhaps, best retained by the Ehizo- 



* Journ. Quek. Micr. Club, iii. (1888) pp. 254-6. 



t Bronn's Klassen u. Ordnungen, i. Protozoa (1888) pp. i.-xviii. 



