78 



COMPARATIVE AX ATOMY 



provisionallj", that this cloaca has arisen by the junction of the terminal portions of 

 the secondary ureter with the rectum, as in other Pulnionata, but that here the pul- 

 monary cavity having atrophied, it opens outward direct, i.e. no longer through a 

 respiratory aperture. Others, again, have tliought the arrangement in Oncidimn 

 and Vaginulus to be primitive, the pulmonary cavity appeariiig here first as an 

 insignificant widening of the terminal portion of the primary ureter. 



If this were the case, then the condition described above (p. 75, 1) for Bv.limus 

 oblongus, whei'e the kidney opens on a papilla direct into the base of the pulmonary 

 cavity, would be thus explained : the pulmonary cavity would have to be considered 

 as a much widened primary urinary duct. Then, in this primary ureter (pulmonarj' 

 cavity) Avould follow the successive stages of the development of the secondary 

 ureter, at first an open and later a partially closed channel, and finally a closed 

 tube, so that at last, as in Helix pomatia, the primary ureter is divided into two 

 distinct portions, viz. the much widened pulmonary cavity and the secondary 

 ureter. But in the Limnceidce, for example, the pulmonary cavity admittedly 

 corresponds with the mantle cavity of other Gastro})ods. The Pulnionata would 

 thus fall into two groups, the Nephroimeusta {Stylo)iimato2)hora), in which the 

 pulmonary cavity = the widened primary ureter, and the BranchiopTieusta {Basom- 

 matophoj'a, p. parte), in which the pulmonary cavity = the mantle cavity of other 

 Gastropods. 



We consider this view incorrect because of the uniformity of the whole organisa- 

 tion in the PiUmanata, and especially because of the occurrence of an osphradium in 

 the pulmonary cavity of a StylommatopJiore {Nephrop7iev.sta), viz. in the genus 

 Testacella. For the osphradium invariably belongs to the mantle cavity, being 

 primitively connected with the ctenidium, it never lies in the urinary duct. 



3. Gastropoda Opisthobranchiata. 



We can here speak of a pallial comijlex only in connection with the Tectihranchia, 

 since in them alone is a distinct mantle fold developed on the right side of the 



Fig. 75. — Aplysia, right aspect, the riglit parapodium (15) turned downwards ; the pallial 

 complex Is seen under the mantle fold 7 (after Lankester). 1, Anterior tentacle ; 2, eyes ; 3, 

 posterior tentacle (rhinophore) ; 4, left parapodium ; 5, seminal furrow ; 6, genital aperture ; 7, 

 mantle fold ; 8, gland ; 9, osphradium ; 10, outline of some inner organ seen through the integument ; 

 11, nephridial aperture ; 12, ctenidium ; 13, anus ; 15, right parapodium ; 16, anterior portion 

 of the foot. (There should be no connecting line between 6 and 0.) 



body. The general order of the organs in the pallial cavity (Fig. 75) is as follows : — 



1. Far back, and often hardly or not at all covered by the mantle, sometimes at the 



summit of a conical prominence, lies the anus, and near it occasionally an anal gland. 



