548 SUMMARY OF CURRENT RESEARCHES RELATING TO 



graphical distribution of the various developmental stages, and with a 

 discussion of the conclusions to be drawn from these. 



The true spermatogonia arc the cells of the peripheral layer. They 

 multiply in that position by indirect division. The spermatogonia grow 

 into spermatocytes (= Henle's cells) each of which, after double division, 

 produces four spermatides ( = sperm-cells). Then a large number of 

 spermatidcs, originating from several spermatogonia, come into associa- 

 tion with a follicular cell ( — Sertoli's cell), and form a spermatogemma 

 ( = spermatoblast). In this finally the spermatosomata ( = spermatozoa) 

 develope from the spermatides. By this von Ebner declares his deter- 

 mination to abide, unless some firmly established counter observations are 

 forthcoming. 



Embryology of Lizard.* — Dr. H. Orr has worked chiefly at the 

 development of Anolis saijrsei, but has also examined some stages of 

 Sphderodactylvs notatus and Liocephalus carinatus. The notochord arises 

 by a diiferentiation of the linear median area of the dorsal wall of the 

 primitive intestine ; and this condition seems to be primitive, for the 

 notochord continues as far as the anterior extremity of the intestine. 

 The mode of development of the notochord and hypophysis seems to 

 point to some peculiar relation between the two organs ; with these the 

 muscular elements of the head are intimately related. At an early 

 stage there is seen to be a median connection of the head-cavities and 

 notochord, which the author proposes to call the coelenteric zone. The 

 first appearance of the tip of the notochord, the coelenteric zone and 

 head-cavities, is in the form of a small mass of cells, apparently budded 

 from the hypoblast. This mass is fused with the epiblast. In some 

 individuals the notochord and cojlenteric zone separate from the epiblast 

 at the same time, though retaining connection with each other. In other 

 individuals the ccelenteric zone separates from the epiblast much earlier 

 than does the notochord, and disappears ; while the notochord remains a 

 long time connected with the epiblast or hypophysis. 



The oral fusion of epiblast and hypoblast is etfected very early. The 

 gill-cleft rudiments first appear as paired pouch-like protrusions from 

 the dorso-lateral parts of the alimentary canal ; the first and second are 

 the first and second clefts, and are the first to acquire an external open- 

 ing ; then, in order, the third and fourth, but the fifth rudiment docs not 

 seem to get an external opening. The part of the alimentary canal from 

 which the gill-clefts open is, comparatively, extremely large. On the 

 ventral surface of the large gill-chamber the first rudiment of the thyroid 

 gland appears. In horizontal section it has a circular outline ; it is a 

 compact thickening of the wall of the gill-chamber, and its cells arc 

 arranged radially. The caudal intestine appears to continue to grow in 

 the ncurenteric region, even after its anterior part behind the anus has 

 atrophied ; this atrophy obtains from before backwards, and for a time 

 the proximal end seems to atrophy about as fast as the distal end grows. 



The segmentation of the mesoblast into somites is efiected from before 

 backwards, and the first somite appears at just the distance behind the 

 ear that would equal the space occupied by one somite. With regard 

 to the mode of origin of the segmental duct, about which much has been 

 recently written. Dr. Orr states that near the region of the neurenteric 

 canal, opposite that part of the unsegmented mesoblast which has not 



* Jouru. of Morphology, i, (1887) pp. 311-63 (5 pis.). 



