DEVELOPMENT OF THE EMBRYONIC RUDIMENT LOLIGO. 255 



a circular swelling such as foreshadows the development of the arms 

 in L. wdynrits (Fig. 116 B, dr). Further, in L. vulgar is, the indi- 

 vidual arms develop more distinctly in consecutive order, the first, 

 which appear as button-like prominences, being those which lie next to 



au 



/rff. 



hit 



au 



FIG. 116. Various stages in the development of Loligo vulgaris (original). A, early 

 stage at which the eyes and the shell-gland appear ; B, seen from the oral side ; O 

 and D, from the anal side. I) is seen obliquely from above, and for the sake of 

 clearness, rather more of the yolk-sac is shown in this figure than is actually visible. 

 ar, rudiments of the arms ; a r a& first three pairs of arms ; au, rudiments of eyes, or 

 the swellings that carry the optic pits ; d, yolk ; ds, yolk-sac ; htf, posterior funnel- 

 folds ; k, gills ; between the two branchial prominences lies the rudiment of the anus ; 

 m, oral aperture ; ma, mantle ; ot, otocysts ; r, edge of, the blastoderm ; sd, shell- 

 gland ; vtf, anterior funnel-fold. 



the funnel. At this period, the rudiments of various other organs are 

 already visible, the most striking of these being the paired branchial 

 fold (Fig. 116 C, k) which lies immediately in front of the mantle 



