ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 601 



Dr. Vosmacr believes that the oldest sponges were deep-sea forms, and 

 that a consequence of their living in shallow regions has been an arrest of 

 development, the skeleton degenerating and the variety of spicular forms 

 being gradually reduced. 



The most primitive forms of the Calcarea were, possibly, Olynthus-like ; 

 these gave rise to the Asconidte and the ancestors of the Syconidaa, as well 

 as to the Leuconidse and Teichonidae. The primitive form also gave rise 

 to the Siliceous Sponges with triaxonid spicules ; thence the Hyalospongiae 

 and the Tetraxonina. The hyalospongine stock gave rise to the Lithistina, 

 GeodidaB, and Ancorinidse ; from the last arose the Plakinida) and Corti- 

 cida), and doubtless also the Chondrosidae and Halisarcse ; the main stem 

 degenerated and gave rise to the Halichondrid?e ; the appearance of spongin 

 rendered spicules superfluous, and thus appeared progressively the Spongidae, 

 Aplysiuid^, and Darwinellidfe. 



Reproductive Elements of Spongida.* — Mr. H. J. Carter has an essay 

 on the reproductive elements of sponges, in which he gives some information 

 as to the structure and position of the ovum in Chondrosia spurca, and the 

 history of some of the discoveries connected with this subject. 



Protozoa. 



Biology of Astasia ocellata and Euglena viridis-t — M. W. Khawkine 

 finds that Astasia ocellata sp. n. and Euglena viridis resemble one 

 another in each being a naked cell of almost the same form and size, 

 whose body is composed of ectoplasm and endoplasm. The former is a closed 

 sac of elongated form (fusiform, or acutely or conically cylindrical), with 

 a small orifice at its anterior end which leads into a j)harynx ; one flagelli- 

 form filament is attached to one of the walls of this canal. This sac is 

 impregnated to a certain extent with elements which do not undergo 

 putrefaction, and according to the forms of contraction, we may attribute 

 to it a muscular structure, the fibrils being disposed in a manner suitable 

 to independent contraction. The form and disposition of these fibrils are 

 not the same in the two organisms ; in Euglena viridis they are longitudinal 

 and annular, and the latter are only found in the anterior part of the body ; 

 Astasia ocellata has annular fibrils only, and they extend from one end of 

 the body to the other. The endoplasm of Astasia is characterized by the 

 thickness of its consistency and by its iminobility, and this appears to be 

 the cause of the diversity of its form in various stages of development ; in 

 Euglena, the endoplasm is less compact, and changes its place more easily ; 

 but in this point various species of Euglena diifer. In both forms there is 

 a nucleus, nucleolus, and accessory elements; the last, in Astasia, being 

 limited to small granules, which appear to be the organs that elaborate the 

 grains of paramylon ; Euglena viridis has none of these small granules, and 

 the grains of paramylon depend either on the plasma (or chromatophores), 

 which are situated at the centre of the body. Here, again, Euglena presents 

 some variations, for in some the part in question is single, in others double, 

 and in yet others the grains of paramylon appear notwithstanding its 

 absence. Like all colourless protoplasm, that of Euglena and Astasia is 

 easily able to appropriate to itself assimilable organic products ; this 

 process, as well as the contrary one of waste, obtains more largely in the 

 endo- than the ectoplasm, and provokes, during abundant nutrition, an 

 unstable equilibrium and a positive pressure between the contents and the 

 surface. In periods of famine there is a " vegetative pressure " between 



* Ann. and Mag. Nat. Hist., xix. (1887) pp. 350-60. 

 t Auu. Sci. Nat., i. (1887) pp. 319-76 (1 pi.). 



1887. 2 R 



