ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 941 



notochord extends as far as the anterior end of the hypophysis ; during 

 development the chord becomes so enclosed by the cartilaginous 

 chordal sheath that it persists only as an irregular stellate mass in 

 the centre of the biconcave bodies of the vertebra?. The subchordal 

 rod is formed of mesodermal cells, and in embryos 15-20 mm. long it 

 unites with the cells of the skeletogenous sheath of the chord, in the 

 formation of which it takes part. This sheath is derived from those 

 cells of the splanchnopleure, which become separated off when the 

 somites are formed ; it is absent within the shell when the membrana 

 propria is alone developed; beyond it the sheath touches and is not 

 separated from the connective-tissue cells which arise from the 

 somites. In the cells of the sheath secondary formation of cartilage 

 occurs, and the cells surround it in a plexiform fashion, while cal- 

 careous salts become deposited in the plexus. In the embryo the 

 skeletogenous layer forms an important part of the vertebral column, 

 but in the adult it only forms delicate calcified rings within the 

 vertebra?, and an important part of the intervertebral portion. 



Reproductive Elements of Myxine glutinosa.* — Mr. J. T. Cun- 

 ningham rinds that the firm membrane inclosing the ripe deposited 

 ovum of Myxineis a primary egg-membrane produced within the follicle, 

 and that the polar threads are processes from this membrane. The 

 membrane itself is single, and, as it has minute pores perpendicular 

 to its surface, it is a zona radiata ; it is homologous with the single or 

 double zona radiata of Petromyzon and of Teleosteans. At that pole 

 of the ovum at which the germinal disc is situated the membrane is 

 perforated by a micropyle.; this last is produced by a process from 

 the follicular epithelium. The immature testis of Myxine consists of 

 a thickened border of the mesorchium containing more or less spheri- 

 cal capsules, which are filled with hyaline nucleated spermatoblasts ; 

 a large proportion of immature Myxine are hermaphrodite, the 

 posterior portion of the reproductive organ containing testicular 

 capsules, similar in structure to those of the male ; in these, but not 

 in the male, the author found spermatozoa ; the males are very rare. 



Development of Fundulus heteroclitus.f — Mr. J. A. Ryder 

 finds the zona radiata of the egg especially well developed, and 

 thickly covered with very fine filaments which have not hitherto 

 been noticed in any Cyprinodont fishes, though known in Belone, 

 Exocsetus, and others. By the intertwining of these filaments the eggs 

 are bound together, and are suspended to seaweeds, &c. The oil- 

 globules are small, numerous, and situated a little to the side of the 

 blastodise. 



Development of the Mud-minnow, t — The ova of this species are 

 laid singly, and adhere to aquatic plants by means of their general 

 coating. Mr. J. A. Ryder finds a group of small oil-globules imme- 

 diately below the blastodise, which become, as the latter extends, 

 more and more scattered over the surface of the ovum. There is a 

 very active amoeboid movement of the substance of the yolk at the 



* Quart. Journ. Micr. Sci., xxvii. '1886) pp. 49-76 (2 pis.). 



t Amer. Natural., xx. (1886') p. 824. J Ibid., pp. 823-4. 



