BROOKS AND RITTENHOUSE: ON TURRITOPSIS. 
451 
finely pointed needle or with a very delicate scalpel the blastomeres 
could be cut or torn apart without being crushed. After they were 
divided, they were flooded from the glass plate by water from a pipette 
into a dish of seawater, and watched in their development. The 
advantage of separating the eggs on a glass plate is that they are held 
slightly by surface tension, and do not rotate as readily while being 
cut apart. Eggs were divided during different stages of cleavage 
from two to six hours old. They were then placed under conditions 
as nearly as possible like those under which the undivided eggs devel¬ 
oped. Unfortunately, as these experiments were incidental and 
incomplete, no eggs were divided during the two-cell stage and their 
cleavage followed in detail. Some eggs that were laid between 5 and 6 
in the morning were divided at 10.45 a. m. More than one half of the 
fragments continued to develop and by 6 o’clock in the evening had 
reached the free-swimming stage. They were retarded a little in their 
development; whole eggs usually arrive at this stage at about 4 to 
4.30 P. m. They were slightly smaller than embryos from whole 
eggs, but apparently just as active and normal. By the next morning 
they had reached the elongated planula stage and were in good condi¬ 
tion, swimming at the surface of the water. 
At another time some younger eggs were divided. These showed 
practically the same results in development. The opacity of these 
embryos made the study of their minute structure impossible during 
life; and because of scarcity of material none could be preserved to 
study their histology from sections. However, these few incomplete 
experiments show that fragments of the egg of Turritopsis are capable 
of developing into apparently entire and normal embryos of slightly 
smaller size. 
Hargitt artificially divided some Pennaria eggs during the first 
cleavage and figures a number of resulting segmentation stages, which 
are very similar to those of whole eggs. He says: “As will be seen, 
each of the resulting halves behaved in a manner indistinguishable 
from that of normal eggs. These half embryos were followed through 
the entire process of cleavage and through the later metamorphoses 
into planula and polyp, and in every respect, size alone excepted, 
the processes were perfectly normal.” 
To my knowledge Haeckel was the first to publish the statement 
that halves of hydromedusa eggs would develop into normal embryos. 
For some time naturalists in general were inclined to doubt the fact; 
