374 



WILLIAM PATTEN. 



which he regards as the remnants of a medianly coalesced 

 gastrula. According to my observations, the mouth, the 

 primitive streak, anus, and the neural canal, are totally inde- 

 pendent organs, and appear at widely different stages. 



Out of a large number of embryos, a few are provided at 



^ 0° "ooOoooo" 





Fig. 18. — A. Diagram to show distribution of mesoderm and endoderm 

 in young embryo of Limulus. m. b. Peripheral zone of mesoderm (?)• 

 m. s. Mesoderm underlying the ventral plate, o. e. Mass of transient 

 endoderm at inner end of oesophagus. B. Slightly diagrammatic view 

 of Limulus embryo. C. Cross section of same through primitive streak. 

 D. Ditto, a little older stage than C. I. e. Lateral eyes. ?«. b. Meso- 

 dermic (?) bands, m. s. Mesoderm. s. o'-". Thoracic sense-organs. 

 p. s. Primitive streak. x* Masses of cells passing inward from the 

 ectoderm. 



the posterior end with an enormous depression, either circular, 

 oval, or pyramidal in outline, at the bottom of which, or on 

 its anterior wall, lies the primitive streak. It is not accom- 

 panied by any special modification in the development of the 



