336 A. Hyatt — Larval Theory of the Origin of Tissue. 



the principal seat of assimilation from the endoderm to the 

 mesenchyme. This transfer possibly occurred during the genesis 

 of Sycones. and other higher forms. 



The researches of Saville Kent among Protozoa have shown 

 that the collar and fiagellum are feeding organs and we must 

 imagine them as having a similar meaning in the internal cav- 

 ity of Ascones, the lowest forms of sponges. 



When we consider the whole series of transformation of the 

 ovum it becomes apparent, that it is at first an autotemnon 

 having the amoeba stage well and clearly developed. The 

 ovum develops parallel with the spermatocyst through the period 

 of division of the nucleus into two parts, the masculonucleus 

 and the feminonucleus. We have tried, in common with some 

 other authors, to show, that the masculonucleus is probably 

 thrown off in the polar globules during a process of agamic 

 division of the nucleus and that these are the homologues of 

 the masculonuclei excluded from the spermatocyst after having 

 been transformed into spermatozoa. 



The remarkable essays of Professbr Ed. Van Beneden on 

 the bisexual nature of the nucleus are the only embryological 

 writings which produce the proofs of this hypothesis in illus- 

 trated form. This author (Fecund. Maturat. de L'ceuf, Archiv. 

 de Biol., torn, vi, 1883) advances precisely similar views to 

 those of Dr. Minot, and shows the phenomena of fecundation 

 and the double composition of the maritonucleus in a series of 

 remarkably clear illustrations. Van Beneden claims to be the 

 discoverer of the bisexual composition of the nucleus of the 

 ovum and refers to his paper of December, 1875 (Bull. Acad, 

 de Belg., 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 Professor Yan Beneden was 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 conjuga- 

 tion 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, and is, therefore, proba- 

 bly bisexual. This statement includes all the basal facts of 

 the genoblastic theory, with, however, two important excep- 

 tions. It omits any notice of complementary behavior or func- 

 tions 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. 



