366 SUMMARY OF CURRENT RESEARCHES RELATING TO 



an explanation for its presence is to be found in the supposition that 

 the renal sac underwent division in consequence of the development 

 of the new gill and the correlated appearance of a second branchial 

 artery. 



If Grobben's view of the origin of the double kidney be correct, 

 it follows that the two kidneys on either side of the body of Nautilus 

 correspond to the single kidney of the Dibranchiata. The great 

 cavity which contains the heart, stomach, and genital gland is, as 

 Vigelius has already shown, the homologue of the secondary coelom of 

 the rest of the Cephalopoda ; and it is a matter of fact that the 

 development of this cavity is similar in Sepia and in Nautilus. The 

 author agrees with Lankester and Bourne in regarding the pyriform 

 appendage of Owen as the rudimentary genital duct of the left side. 



The secondary coelom of the other Mollusca is next discussed. 

 It is shown that in Sepia this cavity is a large space which commu- 

 nicates with the kidneys by the two ciliated funnels, that it is lined by 

 epithelium and contains in its anterior part the heart with its aiferent 

 and efferent vessels, the branchial hearts, and the pericardial gland ; 

 and in its hinder part the genital gland and the stomach. Between 

 the two halves there is an incomplete septum. If we carefully bear 

 in mind these relations, it is not difficult to discover the secondary 

 coelom of other molluscs. It may be seen both in Gastropods and 

 Lamellibranchs, where the epithelial investment of the pericardium 

 has already been detected by various observers. In the former 

 (e. g. Helix) it contains the heart and its auricle, in the latter (e. g. 

 Naiades) the heart and auricles and part of the intestine. This peri- 

 cardium, however, is not the sole homologue of the secondary coelom, 

 the cavity of the genital gland must be also regarded as being origin- 

 ally a portion of it, just as it is permanently in Sepia. 



Another organ which, in the Lamellibranchs, also belongs to the 

 coelom is the reddish-brown organ of Keber, which is made up of 

 cseca lined by an epithelium which is a direct continuation of that of 

 the pericardium. It may be regarded therefore as the homologue of 

 the pericardial gland of the Cephalopoda and have the same name 

 applied to it. It has probably an excretory function. 



In the Solenogastres, as Hubrecht has already pointed out, the 

 body-cavity is much reduced; the only modification to be made in 

 his account is to include the cavity of the genital gland as part of 

 secondary coelom. In Chitons the space is larger and incloses part 

 of the digestive tract. 



After a summary of the views of preceding naturalists on the 

 affinities of the Cephalopoda, Grobben states and expounds the view 

 that Dentalium is the remnant of a primitive form from which the 

 Cephalopoda took their origin. Dentalium resembles them in its only 

 slightly disturbed bilateral symmetry, its elevated visceral sac, and 

 in the development of the pallial cavity behind that sac ; it differs 

 especially in having the mantle cavity open above. Other resem- 

 blances are pointed out in detail. The characters of Dentalium justify 

 the establishment of a separate group of Solenoconcha. 



Grobben does not agree with those who regard the Pteropoda as 



