Supernumerary Sperm Research Articles

THE EARLY DEVELOPMENT OF THE PIGEON'S EGG, WITH ESPECIAL REFERENCE TO THE SUPERNUMERARY SPERM NUCLEI, THE PERIBLAST AND THE GERM WALL

1. The supernumerary sperm nuclei migrate into the potential periblast and disappear between ten and twelve hours after fertilization.2. The position of the cleavage cavity is indicated by the first horizontal cleavage.3. After the disappearance of the sperm nuclei, the marginal cells open peripherally and the periblast becomes organized with nuclei derived from the cleavage nucleus.4. Cells are added to the blastodisc from the marginal and central periblast.5. The "free nuclei" under the blastodisc are periblast nuclei. They are the nuclei of the germ wall, including the Randwulst.

ON THE DEVELOPMENT OF PARASITIC COPEPODS: PART II

1. My observations on the cell lineage agree in general with those of Pedaschenko (who worked it out to the 16 cell stage) save in regard to the orientation. Pedaschenko used no means to distinguish between the two flat sides of the egg and was mistaken in regard to the location of the animal pole, as I have shown (p. 50). At the fifth cleavage the yolk cell buds off the last protoplasmic cell, which is the primary germ cell. After extrusion of the germ cell (32 cell stage) the yolk cell is purely entoblastic. The segregation of the entoblast takes place one generation later than in Lepas (Biglow `02), and the segregation of the germ cells one generation later than in Cyclops (Haecker). The delay in the segregation of these two elements is probably due to the large amount of yolk present and the compressed condition of the egg, which cause delay in gastrulation (epibole). It is probable that all the mesoderm arises from cells turned under the lip of the blastopore.2. The entrance of supernumerary spermatozoa into the egg so greatly disturbs the process of development that the latter is either prevented or so distorted that it never progresses very far, and then in an abnormal manner.3. The compressed condition of the egg affects the cleavage: (1) by altering the arrangement of the protoplasmic cells, (2) by necessitating increased length of the spindles in the yolk cells, (3) by preventing cleavage of the yolk, and(4) by increasing the surface of the egg and retarding gastrulation (epibole). But it is very improbable that slight alterations in the amount and direction of compression have as great an influence on development as supposed by Schimkewitz. I found nauplii which were apparently normal (save perhaps in size) hatching from hemispherical eggs. As the nauplius hatches it immediately rounds up, and assumes the same form whether it arise from a hemispherical or from a very flat egg.