M. Ussow's Zoologico-Embryological Investigations. 209 



splendid addition to the elucidation of Australian natural his- 

 tory ; and it is to be ho})ed that another grant will be made 

 by our liberal Legislature to enable the author to finish his 

 great undertaking. 



XXVIII. — Zoologico-Embryological Investigations. 

 By M. Ussow. 



[Continued from p. 113. J 

 IV. Appearance of the Organs. 



We may now pass to the second period *, that of the pro- 

 duction of the organs. On the first day of this period (in 

 Sepiola and Loligo the ninth day from the beginning of the 

 process of segmentation) the rhomboidal groove already de- 

 scribed gradually becomes deeper, and covered over by the 

 elongate-ovate constantly growing fold, which is separating 

 by constriction at the ventral side and assuming the form of 

 a shield. Towards the end of this period the margins of the 

 fold begin to grow together, and the rhomboidal groove 

 becomes converted into a flat tube, somewhat broader in the 

 middle (especially in Sepia). 



The scutiform hill-like elevation (originating from the co- 

 alesced fold) which lies over the tube chiefly on the dorsal 

 surface, and which is gradually constricted, is the rudiment 

 of the mantle ; whilst the os Sepice will subsequently be 

 formed in the above-mentioned tube closed at both ends and 

 widest in the middle {Sepia, Loligo , Sepiola, Ommastrephes, 

 Rossia). The elevation, separating by constriction at the 

 ventral side, grows both upwards and downwards, and ac- 

 quires first the form of a cup and then that of a cylinder. 



The walls of the so-called primitive groove f, which is con- 



* In Loligo, Sepiola, and Argonauta the second period of development 

 lasts five days. In this paper I follow MetschnikofTs di\-ision of the 

 development of the Cephalopoda into three consecutive periods : — first 

 the formation of the germ-lamellfe ; second, the appearance of the 

 organs ; third, the gradual fuiiher development of the organs. 



t The position of this rhomboidal depression upon the dorsal surface 

 its early appearance (before all the organs), its further mode of develop- 

 ment, are all facts which remind us of the primitive groove of the Verte- 

 brata : and taking them into consideration, it may likewise be called the 

 primitive groove, although as a matter of course there can be no question 

 of comparing it more closely with the primitive groove of the Vertebrata, 

 as the two rudiments represent fundamentally different organs. Althouo-h 

 a groove is also at first formed in the Octopoda (Argonauta), this does 

 not become closed (except in the genus Cirrhoteuthis ? ), but becomes gra- 

 dually effaced and finally disappears entirely. With regard to Arqo- 

 uaida, I must remark that Kiilliker has described and figured the groove 

 (A c. p. 10.'}, Taf vi. tigs. 71-7.'j) as " a rather deep, funnel-shaped pit.'' 



