306 Elliot R. Downing, 



narrow elongated stalk of egg substance held by the contracted 

 ectodermal tissue. The egg, lying- naked in the water is now 

 fertilized."' 



Since Kleinenberg's discoveries some additional facts have 

 been made clear. Korotneff maintained and attempted to prove 

 by the staining reactions that the psendozellen are the modified 

 ingested nuclei of the interstitial cells. G. Entz and K. Brandt 

 demonstrated that the green bodies of H. viridis are algae, Zoo- 

 chlorella conductrix. 0. Hamann the same year, 1882, saw their 

 migration from the endoderm into the egg. thus correcting Kleinen- 

 berg's error in his description of the origin of the green bodies in 

 the egg. Pfitzner first recorded the multiplication of the neuro- 

 muscular cells of hydra by mitosis. jSussbaum showed that the 

 interstitial cells also multiply by this method: his paper, largely a 

 summary of preceding results, as far as the ovogenesis is concerned, 

 adds valuable details as to the method of ingestion of the inter- 

 stitial cells by the egg. 



Brauer makes many discoveries, especially regarding the 

 maturation phenomena: I quote from his paper, translating freely, 

 as follows: "'During the formation of the polar bodies the form of 

 the egg changes from biscuit shape to globular: when this form is 

 attained one may be sure that the polar bodies have been formed. 

 Only a few minutes elapse however before the egg again broadens 

 and at the animal pole a little projection is thrust up between the 

 cells of the ectodermal sheath. Instantly the latter parts; through 

 the orifice there first runs a homogeneous mass which, as soon as 

 it comes in contact with the water, absorbs it greedily. This does 

 not disappear in the water, as Kleinenberg maintains, but remains 

 as a gelatinous sheath about the egg, usually during the whole 

 cleavage process. Similarly the egg flows through the opening, 

 possibly forced out by contraction of the ectodermal covering, 

 possibly through pressure exerted by the swelling gelatinous matter 

 about it or it may be emerging through its own activit}'. Shortly 

 after the rupture of the ectodermal cover, there appears at the 

 animal pole a small but distinct pit. If the microscope is focussed 

 upon this one may see one of the spermatozoa which are swarming 

 about the egg disappear in this depression. Whether the gelatinous 

 coat also has an opening at this point I can not say: no vitelline 

 membrane is formed but the end of fertilization is marked by the 

 disappearance of this depression." 



