ENTOMOSTRACA. 



147 



Hathke, No. 89, and Van Beneden, No. 17), in which a short 

 ventral germ-band is already clearly distinguishable from a dorsal 

 mass of yolk. 



With regard to the order in which the body-segments develop, 

 the general rule is that the rudiments of the most anterior segments 

 appear first, while from a budding zone at the posterior end of the 

 body, but in front of the terminal or anal segment, which develops 

 early, new segments are successively formed. The pairs of limbs 

 develop correspondingly from before backwards, although some 

 variations in the time when the limbs appear are to be found in 



Fio. 72.— Three embryonic stages of Moina recticostris, side view (after Grobben), consecutive 

 to the stages in Fig. 58, p. 124). A, Nauplius stage. B, stage with four thoracic limbs and 

 the first rudiments of the shell (cephalic carapace). C, stage with five thoracic limbs and 

 the two pairs of maxillae, a', first antenna ; a", second antenna ; af, anus ; en, entoderm ; 

 / 7 >/ 77 > f //f , etc., first, second, third, etc., thoracic limbs (in C, with the rudiments of Ihe 

 branchiae); g, genital rudiment; gh 1 , primary brain; gh", secondary brain; vi, mouth; 

 md, mandible ; vis, mesoderm ; vix 1 , first maxilla ; mx", second maxilla ; n, nuchal gland ; 

 ob, upper lip ; oe, oesophagus ; s, shell ; sch, neural plate ; sd, shell-gland ; za, compound eye. 



the different regions of the body. The Nauplius limbs, for instance, 

 often appear simultaneously or in quick succession, and the Nauplius 

 stage is generally distinguished by a period of rest (and frequently 

 by the development of a larval cuticle), while the posterior limbs, 

 •characteristic of the later stages, usually develop in regular suc- 

 cession. In the Phyllopoda, where the maxillae are but feebly 

 developed, these limbs appear very late, when the embryo is fully 

 -developed (Fig. 72 B and C, Zaddach). 



