222 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
To recapitulate. Jn the impregnated egg of Ciona two archoplasmie 
masses can be recognized, one in connection with each of the pronuclei, 
That derived from the spermatazoön is much the more energetic of the two, 
and is alone concerned in bringing the pronucler together. While the pro- 
nuclei are still a considerable distance apart, the male archoplasm divides 
into two distinct attraction spheres, between which the first cleavage spindle 
later forms. The female archoplasm degenerates, taking no part whatever 
in the formation of the first cleavage spindle. There is accordingly in the 
Jertilization of Ciona no union of male and female archoplasms. 
Let us compare briefly these conclusions with those of other recent 
observers on the subject of the attraction sphere in fertilization, 
The fertilization of the Tunicate egg has been studied hitherto by 
Joveri (90) and Julin (’93). Boveri's observations, made on Ciona 
intestinalis and Ascidia mentula, were, as he states, incomplete on 
account of an accident to his preserved material It was his opinion 
that no astral radiations (* Polstrahlungen ") are present in the matura- 
tion of the ogg, and that the two asters of tho first cleavage spindle are 
derived by division from a single one arising in connection with the 
spermatazoón soon after its entrance into the egg. Julin was able to 
confirm on Styelopsis grossularia the observations of Boveri, and to sup- 
plement them, as he says, by demonstrating at the centre of each aster 
of the first cleavage spindle a centrosome. No figures, however, accom- 
pany Julin’s paper; moreover, he states that his observations were 
restricted to two stages, corresponding to those shown in Boveri's 
Tafel XII. Figs. 27 and 29. 
Though my own conclusions are in entire agreement with those of 
overi and Julin as to the derivation of the attraction spheres of the 
first cleavage spindle exclusively from the spermatazoón, my observations 
differ from theirs regarding certain minor points, as the reader may 
learn by consulting the papers cited. 
On the subject of fertilization in groups of animals other than the 
Tunicata there is an enormous literature, I shall refer to only a few of 
the most recent papers. 
In 1891 Fol described the famous “quadrille of the centres” as occur- 
ring in the fertilization of the sea-urchin egg. According to his account, 
there arises in the egg from the tip of the spermatazoón, a centre of 
attraction (“spermocentre”), which later divides. In connection with 
the egg nucleus appears another centre of attraction (“ovocentre”), 
which likewise divides. Upon the meeting of the pronuclei, each half- 
spermocentre unites with a half-ovocentre to form an astrocentre. The 
