XI. INSTRUCTION. 985 



3933b. Collection of Preparations on the Embryology 

 of the Sterlet ((Acipenser ruthemts). 



Ph. Owsiannikqff] University of St. Petersburg. 



< Most of the preparations represent tranverse sections of the eggs or the 

 embryos, hardened in chromic acid, and partly coloured with carmine. 



1. Ripe but not fecundated egg. 



2. Embryo, taken from the egg thirty-seven hours after fecundation. 



3. Embryo, about forty hours after fecundation. 



4. Transverse section of an embryo of thirty-seven hours. 



5. Transverse section of an embryo of forty-eight hours. 



6. Section of the brain and the eye-vesicle of an older embryo. 



7. The three embryonal plates. 



8. Section through the nerve-ganglion ; the rudimentary gills are to be 

 seen. 



9. This section represents the cells that form the medulla spinalis, chorda 

 dorsalis, and other parts. 



10. Section through the head of a sterlet just coming out from the egg- 

 shell. 



11. Sterlet about three days after coming out. 



12. Sterlet about a week. 



13. Some longitudinal sections of a one week's sterlet. We see the eyes, 

 the heart, the intestinal canal, particular nervous organs of the surface of the 

 head. 



14. The segment. 



15. 16. The spinal furrow and the first plates. 



17. The closing of the spinal furrow ; the plates are not completely 

 formed. 



18. Longitudinal section through an embryo in the egg-shell. The in- 

 teresting feature of this preparation is the closing of the intestinal canal. 



19. Transverse section of an embryo, formation of muscles, construction 

 of the spinal chord, wolffian body, &c. 



20. Preparation of a coregonus, showing the central nervous system. 



21. Section of an egg of petronzyon fluviatiles, showing the formation of 

 tne intestinal canal. 



3933a. Collection of Preparations of the Nervous 

 System of Molluscs. 



Ph. Owsiannikoff) University of St. Petersburg. 



1-3. Whole nerve-ganglion and two sections, from a thetis. 



4. Aeolis. 



5, 6. Gastropteron. 



7. Bulla, with eyes. 



8. Umbrella. 



9. Pleurobranchus. 



10. Pleurobranchus, section of a nerve-ganglion. 



11. Aplysia. 



12. Lobulus electricus (Eajae). The section is made of a brain preserved 

 for three years in spirit, the cells and fibres are still seen very well. 



13. Dentalium. 



3933c. Eight Drawings illustrative of the minute struc- 

 ture and reproductive process of the Mushroom Tribe. 



W. G. Smith. 



