BROOKS AND RITTENHOUSE: ON TURRITOPSIS. 
and that when it has once entered the substance of the egg, the male 
and female pronuclei are brought together by the attraction existing 
between the two. 
It was impossible to see the discharge of the spermatozoa from the 
males; neither did I see the spermatozoa enter the eggs. Moreover, 
as stated before, the eggs are so opaque that the internal phenomena of 
fertilization could not be followed in the living specimens. There is 
reason to believe that the sperms are discharged at about the same 
time that the females lay their eggs. Fertilization takes place in the 
water immediately following maturation, and segmentation begins in 
a very short time. 
Segmentation. 
Segmentation is total and approximately equal. While there is a 
slight difference in the size of the blastomeres at times, yet this differ¬ 
ence is not constant and they all have the same value in development, 
that is, they are not divided into macromeres and micromeres. There 
is no evidence either from observations of the living eggs, or from the 
study of sections of preserved material that any of the blastomeres can 
be localized as forming distinct parts of the future embryo. During 
the first two or three cleavages the process is usually quite regular, 
but beyond the eight-cell stage the segmentation becomes very irregu¬ 
lar and erratic; almost if not fully as remarkable as that described and 
figured by Plargitt for Pennaria tiarella and of which he says: “Be¬ 
tween the extremes of the embryonic history from the early cleavage 
to the formation of the morula are to be found the most erratic and 
anomalous exhibitions of developmental phenomena which have ever 
come to my knowledge, if indeed its counterpart has hitherto been 
known. It is not strange that with the mental pictures of such steady- 
going exhibitions as are found in the development of annelids, molluscs, 
etc., one should regard such monstrosities as are very inadequately 
represented in the various figures illustrating this paper as abnormal 
to the degree of being pathologic! And thus it seemed to me when 
first observed; and as pointed out in the earlier paper, the first batch 
of eggs were discarded as having ‘gone bad.’” 
' When I first began the study of the development of Turritopsis, 
the irregularities of segmentation struck me as very peculiar and I was 
at first inclined to think that they were abnormal. After I allowed 
