216 M. Ussow's Zoologico-Emhryohgical Investigations. 



treraity ; and a lower one, the perfectly straight rudiment, 

 closed at the extremity, of the true rectum. The walls of these 

 two tubes, as also tlie wsopha^us, consist of a layer of cylin- 

 drical cells of the introverted upj)er lamella, surrounded Ly 

 one or two layers of fusiform cells of the intestino-tibrous 

 layer of the middle lamella. 



The further development of the intestinal canal which takes 

 place in the third period, consists in the continued p-owth and 

 increase in depth of its parts above mentioned. The stomach 

 is formed at first as a dilatation of the hinder part of the 

 oesophagus, which, after it has lengthened parallel to the 

 dorsal part of the mantle as far as one half the length of the 

 latter, bends towards the ventral surface almost at a right angle, 

 and unites* with the lengthened primitive rectum, which is 

 turned up towards the back. 



At the point where the prolongation of the stomach meets 

 the rectum a small dilatation is produced ; and from this the 

 ccecum is afterwards formed. At the close of the first half of 

 the third period, in transverse and longitudinal sections of 

 the Cephalopoda investigated by me, there are behind the ink- 

 sac (which is already considerably developed), and at first 

 nearer the ventral surface of the embryo, two blind, clavate, 

 thick-walled tubules, which have been developed from a dila- 

 tation of the posterior part of the intestinal canal, and rejjre- 

 sent the rudiment of the live): It is only in the postembryonic 

 period, after the nutritive vitcllus is entirely absorbed, that the 

 two halves of the liver enlarge very ra])idly, ap{)roach each 

 other, and take up their ordinary place in tlie dorsal ])art. 



The proventricuhts, or so-called croj), is also developed in 

 the embryo oi Argonauta in the first half of the third period, 

 as a dilatation of the cesophagus situated beneath the cerebral 

 ganglion. The walls of all the dilatations above mentioned, 

 which originate at different times, are formed from the vari- 

 ous main and subordinate parts of the intestinal tract, and con- 

 sist of one or two rows of fusiform cells of the intestino-fibrous 



connexion between the ink-sac and the liver, formerly described by Van 

 Beneden {loc cit. p. 10), has no existence. 



• I have not succeeded in observinij: the moment of direct union ; but 

 from the evidence of lon<ritudinal sections of certuin sta^'-es, and, in fact, 

 of embryos in which the Ion}? anterior intestine, enlarged at the extre- 

 mity, extends to two thirds the height of the mantle (first half of the 

 third period), and the rectum curves up towards the dorsal surface, and 

 then of certain sections (from the second half of the third period) in 

 which the slightly tortuous tractus intediiKtlis is visible in its whole 

 length, I firmly believe that I may assert that this union in reality takes 

 place. 



