THE DEVELOPME^■T OF THE SQUID. 373 



The external openings of the otocysts have become 

 constricted to long, tortuous, ciliated ducts, which are not 

 visi))le with a low power, and are not shown in the figure. 



The eye-stalks, (es), are of about the same relative 

 length as in the last figure, but the yolk prominences 

 which have filled them up to this time are now almost 

 entirely withdrawn or assimilated, and the cavity of the 

 eye-stalk is nearly filled b}' the ball of the eye (e), the 

 optic ganglion, and the white body. 



The arms have lengthened, and suckers have appeared 

 upon the longest pair (a"), and a new pair (a'), have 

 made their appearance upon the posterior or siphonal sur- 

 face of the body. 



The yolk is now divided into four well-marked regions, 

 the external yolk sac (y ) , which is still nearly spherical ; 

 the head yolk, which is pretty nearly cylindrical, and 

 which passes gradually into the external yolk sac ; the 

 body-yolk, much smaller than the head-yolk, and sep- 

 arated fi'om it abruptly by a well-marked change of 

 outline ; and the little mass of yolk, at the dorsal end 

 of the body, constricted off from the mass by a deep 

 groove. 



Fig. 199 represents a view of the posterior surface of a 

 somewhat older embryo. 



The mantle is now large and bowl-shaped, and covers 

 the greater part of the body dorsal to the eye-stalks. 

 Chromatophores now begin to make their appearance 

 around the posterior side of the edge of the mantle, and 

 those Avhich first appear are of a dark brown color. 



The gills (g), have lengthened considerably, and are 



divided by constrictions into a series of enlargements, the 



dorsal one being: much laro^er than the others, and be- 

 es c 



cominsf the branchial heart. The inner and lateral folds 



