518 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. 



secondary germ (Parablast or Hoemoblast). The account he 

 has given has not, however, been sufficiently proved; and 

 in the course of the subsequent description it will be shown 

 that the observations from which it was drawn permit 

 other significations to be given more conformable to general 

 biological principles. 



The account given by Pander refers to the fertilized laid, 

 but not incubated egg. The commencement of incubation 

 certainly cannot be regarded as the beginning of the process 

 of development. During the passage through the oviducts 

 important processes, from my point of view, take place ; for 

 the cleavage of the germ occurs .here, and the cleavage 

 elements arrange themselves in layers. This lamination has 

 progressed to various stages in different ova at the time of 

 their being laid, and on this account alone it would be 

 disadvantageous to ascribe a definite histological character 

 to this period. 



The cleavage of the germ of the Fowl was first described 

 by Coste * This, however, he did only so far as it can be 

 observed to occur on -the surface. Oellacherf 1 examined trans- 

 verse sections of the yolks of eggs at various stages of 

 cleavage, and in his essay we for the first time meet with 

 an account of the very first traces of the chick. I feel 

 myself compelled therefore to adhere to his statements. But 

 inasmuch as his researches were conducted under my own 

 inspection, the account here given is based in part upon my 

 own observations. 



All the preparations here alluded to were obtained by the following 

 means. The yolks of oviducal eggs, or of eggs obtained during the 

 first day of incubation, were carefully freed from albumen, cautiously 

 washed with dilute chromic acid, the albuminous precipitate as it 

 formed being removed with forceps, and the clean yolk then placed in 

 pure diluted solution of chromic acid. After a few days the segment 

 of the yolk containing the germ membrane was removed, and care- 

 fully placed in alcohol, where it was allowed to remain till the 

 water was as far as possible removed. It was then imbedded. 



* See his Histoire du Developpement des Corps Organises. 

 t Strieker's Studien, 1870. 



