No. 2.] THE EMBRYOLOGY OF THE APTERYGOTA. y 2, 



At almost the same time UzeP published a series of articles 

 on the two forms Campodea and Lepisma. His work on the 

 latter practically confirms that of Heymons and may be omitted 

 from this review. He determines that the eggs of Campodea 

 are spherical, about 0.4 mm. in diameter, undergo superficial 

 cleavage, resulting in a blastoderm spread uniformly over the 

 whole surface. No secondary yolk cleavage exists. The germ 

 band arises by migration of cells from all parts of the blasto- 

 derm to form a belt encircling nearly the whole &gg. A " dor- 

 sal organ " appears between the head and the tail, but neither an 

 amnion nor a serosa is developed. Paired appendages are early 

 distinguished, also a median unpaired labrum. Of the paired 

 appendages the following are found : one pair of antennae, a 

 pair of distinct intercalary appendages, one pair of mandibles, 

 two pairs of maxillae, three pairs of thoracic feet, and nine 

 pairs of abdominal structures. An interesting point is noted 

 in the permanent retention of the intercalary appendages as 

 lateral folds round the adult mouth. Later the i-7th abdomi- 

 nal appendages split longitudinally, the outer part forming the 

 permanent styli and the inner the abdominal sacs. 



There is to appear in the new Journal of Morphology ^^ a 

 paper giving the results of my studies on Annrida maritima. 

 Merely a summary of the most important points will be included 

 in this consideration. It was found that the ovary was ex- 

 tremely simple in form, like that of a myriapod. Each ovum is 

 associated with nutritive cells and the germinal vesicle early 

 disappears. The Q.gg is spherical, about .27 mm. in diameter, 

 with at first slightly unequal holoblastic cleavage ; this is even- 

 tually lost after a large-celled morula stage has been formed, 

 and the blastoderm rises by migration, as in eggs with super- 

 ficial cleavage. It assumes a two-layered condition at once, 

 the entoderm remaining dormant in the yolk. A "dorsal 

 organ " is formed between the two ends of the belt-like germ 

 band, the latter early showing the usual pairs of appendages 



^ Uzel, H., " Vorlaufige Mittheilungen iiber die Entwicklung der Thysanura. 

 Beitrage zur Entvvicklungsgeschichte von Campodea staphilinus," Zool. Aiiz. 

 Nrs. 125, 128, 135. 1877. 



1° Claypole, A. M., " The Oogenesis and Embryology of Anurida Maritima," 

 Journ. of Morph. Vol. xiv. 189S. 



