no. ,.] THE EMBRYOLOGY OF LBtULUS. 53 



Sta^e K Figs. 34 and 35 (Packard, Fig. 25 ; Self, Figs. 16 and 

 ,7) sfhe laftltage previous to the molt which results m the 

 adult form. The abdomen is relatively much larger than before ; 

 te opercular lobes have nearly met in the median hne, and the 

 animal begins to burrow in the sand, although embryos of this 

 stac^e are not infrequently taken in the towmg net. 



Sta^e L (Packard, Fig. 27) is produced from the last by a 

 sin-^le^molt. It is characterised by the presence of an elongate 

 tels°on much like that of the adult. With this stage my studies 



™The following points may also be of interest. The Blasto- 



dermhaut is molted at about Stage F, the fme varying with 



different e-s. It still persists as an embryonic envelope 



Jfcar'ous chorion of Packard) until a late stage. Soon after it 



s shed from the parent cells a second embryonic cuticle is cast, 



and then the true'chorion is shed, and the embryo, encased in 



the distended Blastodermhaut, escapes from the egg at about 



Stage KorL The Blastodermhaut itself is ruptured, and the 



animal begins its free existence at the end of Stage I. 



Comparisons. 

 A With Previous Accounts. - H. L. Osborn ('85) and Brooks 

 and Bruce (85) have described some of the phases of segmen- 

 tation, the latter studying sections. Their account so far as it 

 goes is reconcilable with what I have described, including the 

 pre-se^mental movements. They have also noticed the primitive 

 cumulus and interpret it as giving rise to the mesoderm a pmnt 

 be discussed later. Neither, however, traces the relat'onsh p 

 of the cumulus to the embryo. According to the last quo ed 

 paper the blastoderm is to be regarded as ecto-mesoderm. the 

 yolk as at least largely, if not wholly, entoderm^ 



Packard ('72) has apparently seen some of the phases of seg- 

 mentation, but it is difficult to arrange his account - its proper 

 order, as it is evident that some of his eggs were addled^ In 

 o hers he figures nuclei which had no actual existence. From 

 : tm ntatio'n until the appearance of the limbs Packard has seen 

 no°thin. except the formation of the Blastodermhaut, which he 

 "n various papers has compared to the Hexapod amnion - a view 

 wJch I CM) showed to be untenable. H. L. Osborn's account 

 Tf the formation of the limbs, etc., I have referred to above 



