BROOKS AND RITTEXHOUSE: OX TURRITOPSIS. 451 



finely pointed needle or with a very delieate 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; 



