198 Mr. A. Hyatt on the 



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 probably bi- 

 sexual. This statement includes all the basal facts of the 

 genoblastic theory, with, however, two important exceptions. 

 It omits any notice of complementary behaviour 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. 

 Dr. Minot (Proc. Bost. Nat. Hist. vol. xix. p. 170) proposed 

 to name the original bisexual nucleus "genoblast," the female 

 part " arsenoblast," and the male " thelyblast," and these 

 terms have precedence of those we have advanced, or of those 

 proposed by Van Beneden ; but we have preferred to use 

 names which retain the word nucleus, as more expressive of 

 the true relations of derivative nuclei. 



If this is true the occurrence of this process of excluding the 

 masculonuclei in the ovum during the agamic stage exhibits 

 an earlier inheritance of a characteristic which in the Protozoa 

 occurs only after and as a result of impregnation, except pos- 

 sibly in some of the more specialized Flagellata and Ciliata, 

 where the existence of spermatocysts and spermatozoids leads 

 one to anticipate a corresponding differentiation. The female 

 zoon certainly appears to be in reality an ovum, and to develop 

 like one into a blastula, as pointed out by Biitschli. 



This view includes some results worthy of attention. The 

 concrescence of Protozoons, as in cases cited by Drysdale and 

 Dallinger, and in some plants where the whole contents of one 

 pair of cells or more than one pair of cells are mingled together, 

 is asexual conjugation, but not sexual conjugation. The latter 

 occurs only by the exchange of differentiated parts of nuclei, 

 or between the larva-like spermatozoa and the complementary 

 part of the nucleus in the ovum. Thus such forms as Eudorina 

 and Volvox might be called, on account of their morphology, 

 Blastrea, and could, because of their mode of reproduction and 

 the existence of but one layer in the body-wall, be appropri- 

 ately designated as true Mesozoa. 



With regard to the meaning of the early stages of the ovum 

 we come nearer to Biitschli (Morph. Jahrb. 1884) than any 

 other author, and regard his placula theory as opening a way 

 far more promising than any so far proposed. This author, 

 however, voluntarily rejected the aid of the sponges in his 

 arguments, under tlie erroneous impression that they were 



