CASTLE: EMBRYOLOGY OF CIONA INTESTINALIS. 223 
two astrocentres arise on opposite sides of the cleavage nucleus, and 
between them the first cleavage spindle forms. 
A short time after the publication of Fol’s paper, Guignard (91) 
described as oceurring in the fertilization of a flowering plant a similar 
union of male and female centres of attraction. (“spheres directrices "). 
More recently Conklin (94) has observed its occurrence in the case of a 
mollusk, Crepidula. 
Fols observations, however, are flatly contradieted by the careful 
studies of Wilson and Mathews (95) on three different genera of Echi- 
noderms. They find that “the central archoplasm sphere (‘attraction 
Sphere?) of the cleavage amphiaster is derived by direct and unbroken 
descent from the central mass of the sperm-aster without visible partici- 
pabion of an egg-aster.” 
Fick (93) also observed that in the fertilization of a Vertebrate, Axo- 
lotyl, the centrosomes of the first cleavage spindle are derived exclu- 
sively from the spermatozoön. jrauer (92) arrived at a similar 
conclusion regarding the fertilization of a crustacean, Branchipus, and 
Mead (95) regarding a worm, Cheetopteris. These observations are in 
entire agreement with those made prior to Fol’s announcement of the 
“Quadrille” by Boveri ('88) on Ascaris and Sagitta, and by Vejdovsky 
(88) on Rhynchelmis. Boehm ('88) had also expressed with some 
caution a similar view regarding Petromyzon. 
On the other hand, Wheeler (95), in a paper published simultane- 
ously both with that of Wilson and Mathews and with that of Mead, 
states that in Myzostoma both centres of attraction arise in connection 
with the egg nucleus, none whatever being produced by the spermatozoün. 
Summary on Maturation and Fertilization. 
(1) Zn a majority of the animals in which fertilization has been most 
recently studied the attraction centres of the first cleavage spindle are de- 
rived from the spermatozodn and from the spermatozoón only, 
(2) But in the fertilization of at least one animal, and undoubtedly in 
all cases of parthenogenetic development, the attraction centres arise solely 
in connection with the egg nucleus. 
(3) Both these facts prove conclusively that the archoplasm, or “ organ 
of division,” is not a bearer of heredity, since in fertilization it may be 
derived from the sexual product of one parent only, whereas it is a well 
recognized law that heritable substance is contributed to the offspring by 
both parents equally, 
(4) If the archoplasm is furnished in some cases by the sperm only 
