CEPHALOPODA. 



435 



region of the mantle-cavity (Fig. 348, b). In Dibranchs (Fig. 349) 

 the perivisceral part of the coelom is also in two communicating 

 parts : (1) the genital division, which opens to the exterior by the 

 genital duct, and is related only to the gonad; and (2) th^ viscero- 

 pericardial which has relations to the heart, stomach, intestine, 

 branchial hearts, and pericardial glands (Decapoda), and does not 

 open to the exterior. In Octopoda (Fig. 350) the viscero-pericardial 

 coelom is prac- 

 tically absent, 

 being reduced to 

 a small space 

 ( VI) on each 

 side round the 

 glandular appen- 

 dages of the 

 branchial heart 

 ( pericardial 

 glands), which 

 opens ( VII) into 



the nephridiuill ^ IG ' ^^. Diagram of the coelom of a female Octopus, ventral 



. (posterior) view (from Pelseneer, after Brock). / branchial heart ; 



and COm muni- JI canal connecting the genital and visceral parts of the coelom; 



Cates bv a narrow ^^ oy iducts 5 J^oviducal gland ; V appendage of branchial heart; 



VI perivisceral (pericardial) coelom ; VII reno-pericardial opening ; 



Canal (//) with VIII ovary ; IX genital coelom. 



the apically- 



placed genital division of the coelom. In Dibranchs the perivisceral 

 (viscero-pericardial) part of the coelom also communicates with the 

 kidneys, and not directly with the exterior (Fig. 349, XVII), whereas 

 in Nautilus it has no opening into the kidney. 



The branchiae have the form of two (Dibranchiata) or four 

 (TetrabrancJiiata) bilamellate ctenidia, which are placed on the 

 visceral sac in the mantle-cavity, and are not ciliated. In Nautilus 

 they project freely and the posterior are a little larger than the 

 anterior; in Dibranchs they are attached to the body along one 

 side of the axis. 



Osphradia are absent in Dibranchs, but in Nautilus there are two 

 pairs of papillae in the mantle-cavity, which are supposed to repre- 

 sent them. The anterior pair is between the two pairs of gills 

 (Fig. 348, d), while the posterior osphradia* are the so-called post- 

 anal papillae placed near together on the mantle between the renal 

 sacs and the nidamental glands in the female, and in the same 



* Vide A. Willey, Q. J. M. S., 40, 1897. 



