266 The American Naturalist. [March, 



views regarding the connection of the median anlage of the thyroid with 

 the csecal foramen of the tongue into harmony with the anatomical 

 facts revealed by A. Streckeisen. In this embryo the hyoid comes 

 into intimate contact with the epithelial connection of csecal foramen 

 and median thyroid and is thus well placed for the formation of those 

 inclusions of gland-tubes within the hyoid described by Streckeisen. 

 Incidentally the study of another embryo of 9*1 mm. leads the author 

 to infer that this median anlage may aid in the formation of the lateral 

 thyroids. 



Origin of Spinal Ganglia in Man. 1 — Study of a human 

 embryo of 2'5 mm. leads Dr. M. V. Lenhossek to the follow- 

 ing conclusions: The medullary plate is at first a median 

 thickening of ectoblast with no thin central region to give it a 

 bilateral or double character. The material for the formation of 

 spinal ganglia first appears as a strand of rounded ectoblast cells, not 

 segmented, along each side of the medullary plate. As the medullary 

 plate closes these two strands unite to form a wedge-shaped mass 

 appearing as cross section as the keystone of the closed medullar y tune. 

 Though thus closely united with the tube these spinal gangliau cells 

 grow out again and allow the tube to close a second time without t»«f 

 aid. In this outgrowth the first segmentation appears, the outgrowth 

 being greater in the mesoblastic somite regions, hence the spinal 

 ganglia are from this first appearance intervertebral in position. I^ter 

 stages are not given, but with the aid of sections of chick and of 

 Siredon the author extends the above view to all vertebrates, explain- 

 ing away the difficulties offered by certain observations of others ; 

 harmonizing the ideas of His and Balfour and in general results 

 agreeing with Beard. 



Somites of Human Embryos. 2 — From the embryo mentioned 

 in the last notice and three others of 4'25, 45 and 10'2 mm. and with 

 the aid of a comparative study of some lower vertebrates, J. Kallmann 

 obtains facts and explanations of facts that form an interesting contri- 

 bution to the subject of metamerism in higher vertebrates, though the 

 evidence presented is not all of as convincing a character as might he 

 desired. The chief points may be briefly outlined as follows: 



The myotomes (protovertebne) have at first a cavity, royoccel, 

 which is subsequently filled by an ingrowth of the inner wall. The 



* Archiv. f. Anat. Phys., 1891, 44 pps., 2 Pb. 



