308 CEPHALOPODA. 



must rather imagine it to be a new structure formed from the posterior pair 

 (which alone is originally present). This process may have been connected 

 with the development of four gills, which some believe to be a secondary con- 

 dition and which has led to the assumption that the Tetrabranchia (Nautilus) 

 were derived from Dibranchia (v. Jhering, No. 19). Although Nautilus is, 

 without doubt, a very ancient and primitive form, there are certain signs (e.g., 

 the degeneration of the efferent genital duct) that it was already specialised 

 in a definite direction, and thus might have acquired a second pair of gills. 

 The same argument would apply in the case of the kidney. This view would 

 find some support from the fact that, in other Mollusca, only one pair of 

 nephridia and, with the exception of Chiton, only one pair of gills are present. 



The certain information we possess as to the development of the kidneys 

 is as yet too scanty to enable us to settle this question. It was shown by 

 Bobretzky that, in Loligo, the kidneys arise directly under the covering of 

 the postero-dorsal surface as two distinct sacs in the mesoderm, and only 

 later unite, and assume the close relation to the veins which they show in 

 the adult. The inner wall of the kidneys is much folded, and thus yields the 

 aciniform structures known as venous appendages (Grobben). 



Our knowledge of the development of the genital organs also is still very 

 incomplete. The genital glands arise as thickenings of the pericardial 

 epithelium near the heart (Bobretzky, Schimkewitsch). This primitive 

 relation to the pericardium or coelom is preserved by them throughout life, 

 but at a later period a (genital) capsule is formed round the glands by a 

 peritoneal fold ; the cavity of this capsule, however, remains permanently in 

 connection with the body-cavity, and thus forms a part of the latter (Brock, 

 Grobben). 



The efferent ducts, of which there is one pair, are connected with the 

 capsule. When, as in most Dibranchia, there is only one efferent duct, this 

 must be considered as due to degeneration, as is proved by the presence of 

 paired ducts in the Octopoda, in Ommastrephes (a Decapod) and in Nautilus, 

 this latter form having one functional and one reduced oviduct. 



This relation of the efferent genital ducts suggests that they are modified 

 nephridia (see Vol. iii., p. 42 footnote), and the question thus again arises 

 whether the Cephalopoda possessed two pairs of nephridia and in this respect 

 a segmentation (which, however, would be incomplete). Such a view is by 

 no means justified by what is known of those Molluscs which on the whole 

 show conditions more primitive than those of the Cephalopoda. These 

 Molluscs afford no convincing evidence of segmentation. We must therefore 

 regard efferent ducts as having formed independently of the nephridia, or else 

 as derived by fission from nephridia, but cannot consider them as independent 

 nephridia. 



The blood-vascular system. Even in the case of this system of organs, so 

 well developed in the Cephalopoda, very little is known ontogenetically,* and 



* Bobrktzky appears to have studied the development of the circulatory 

 apparatus in detail, but as his work is in Eussian, we are limited to the 

 descriptions of the figures and a short abstract in Anat. Jahresb. Hofmann 

 and Schwalbe, Bd. vii., 1878, and this applies also to our former references to 

 his observations. 



