1884.] 147 [Hyatt. 



Protozoa, and are ready to seek out and fertilize the female zoon, 

 which in Metazoa is of course the ovum. 1 Their habits, there- 

 fore, sufficiently explain this retention of the agamic, flagellated, 

 primitive form. 



When we consider the whole series of transformations of the 

 ovum it becomes apparent, that it is an autotemnon having the 

 amoeba stage well and clearly developed. The ovum develops 

 parallel with the spermatocyst up to the period of division of the 

 nucleus into two parts, the masculonucleus and the feminonucleus. 

 We have tried, in common with other authors, to show, that the 

 masculonucleus of the ovum is probably thrown off in the polar 

 globules during the stage of agamic division of the nucleus and 

 that this process which is the homologue of that by which the 

 masculonuclei are excluded from the spermatocyst after having 

 been transformed into spermatozoa. 2 



M. O. S. Jensen has combated this theory (Archiv. de.Biol- 

 ogie, Vol. iv, p. 68) on the ground that there is no structural clis- 



*It is here interesting perhaps to note, that this conclusion was formulated before 

 we became acquainted with Butschli's or Carter's researches ( Amer. Nat., Vol. xviii, 

 p. 460, 1884). 



2 We greatly regret the inexcusable carelessness of having omitted to notice the re- 

 markable writings of Prof. Ed. Van Beneden on the bisexual nature of the nucleus. 

 These are the only embryological writings which produce the proofs of this hypothesis 

 in illustrated form, but we were not aware of their existence until too late for notice. 

 Prof. Ed. Van Beneden (Fecond. Maturat. de l'oeuf. Archiv. de Biol. Tome vi, 1883) 

 advances precisely similar views to those of Dr. Minot, and shows the phenomena of 

 fecundation and the double composition of the masculonucleus in a series of remarkably 

 clear illustrations. The author claims to be the discoverer of the bisexual composition 

 of the nucleus of the ovum and refers to his paper of Dec, 1875 (Bull. Acad, de Belg., 

 Ser. 2, Vol. XL, 1875) as containing the first statement of his discovery. Though not 

 pretending to forestall the judgment of those better qualified to decide the merits of 

 these claims, we find that Prof. Van Beneden was probably the first to announce the 

 basal facts of the bisexual theory, but that he did not give all of the essential conditions 

 of the phenomena of conjugation between the male and female parts of the nuclei in 

 his first paper. This author in the work just cited (p. 700) suggests, that the peripheral 

 pronucleus is probably partially formed of spermatic substance, that the central 

 pronucleus is female and that the segmentation nucleus is a compound body resulting 

 from the union of these two nuclei, and is, therefore, probably bisexual. This 

 statement includes all the basal facts of the genoblastic theory, with, however, two im- 

 portant exceptions. It omits any notice of complementary behavior or functions of the 

 useless parts of nuclei in both the spermatocyst and ovum. This essential condition 

 of the conjugation of the nuclei does not seem to have been elaborated by Van Beneden 

 until 1883, long after the appearance of Dr. Minot's paper. I have also to apologize for 

 having overlooked the fact that Dr. Minot (Proc. Bost. Soc. Nat. Hist., Vol. xix, p. 

 170) had already proposed to name the original bisexual nucleus "genoblast," the fe- 

 male part, " arsenoblast," and the male, "thelyblast," and these terms have precedence 

 of those we have advanced above, or of those proposed by Van Beneden. 



