42 MR. 11. OARIS^ER ON THE SHELL-BEARING MOLLUSCA. 



acoustic spot and a minute ganglion upon it ; behind, this lower 

 portion consists of five ganglia connected with both the anterior 

 and upper swellings b j a cord, but separated from the former by the 

 aorta, as usual, and giving nerves to the flanks, pulmonary orifices 

 and sac, heart, stomach, and viscera. The lower ganglia are bright 

 yellow. 



With respect to the Pteropoda, the branchiae in Hyalcea exist 

 as a delicate membrane under the swollen part of the shell, in 

 structure much like the same part in the Ascidians, the inlet being 

 through the anterior opening of the mantle. There are eyes at the 

 fold of the mantle behind, and two small tentacles above the mouth ; 

 the heart and rectum being on the left side, and the generative 

 opening at the base of the right ala. Cleodora is a very beautiful 

 creature, with the same disposition and structure of viscera; 

 brain-spots but no eyes were visible ; the mantle had beautiful 

 muscular bands ; the branchiae as above ; the buccal apparatus is 

 imperfect in both. Cleodora has similar membranous expansions 

 with Hyalaa, and also a sort of triangular lip. 



Argonauta has a lachrymal pore before and beneath the eye. 

 The beautiful and obvious respiratory mechanism in the Cephalo- 

 poda needs not to be described. There is a large sac behind the 

 viscera of the Argonaut, which opens on each side ; it is perhaps of 

 some hydrostatic use. There are at least three pairs of salivary 

 glands, of which four open on the floor of the mouth, and two or 

 three at the commencement of the gullet. Several small shells of 

 Pteropoda and fragments of Cephalopods were found in the sto- 

 mach, on which was observed the large nervous ganglion found in 

 all these, as well as in lower mollusks. The branchial nerves have 

 each two ganglia, of which the last at the root of the branchiae is 

 rounder than the other ; the branchial hearts have processes as 

 in ^e]^ia. In Hepia two openings lead from the respiratory sac 

 into the cavity containing the venae cavae and their secreting ap- 

 pendages often imbued with glittering crystalline particles, and 

 from the above cavities a wider opening on each side leads into a 

 second sac further back, situated in front of the shell. There are 

 auditory sacs in the Argonaut, The oviducts have separate open- 

 ings, but originate together. Both ^e'pia and Argonauta are infested 

 with a subcutaneous filiform entozoon, hooked anteriorly and rolled 

 up spirally in the former. Loligo media and Sepiola have but one 

 oviduct, and the two large, glandular, laminated organs, opening 

 at their summits, are wanting in Argonauta and Octopus. In 

 Sepiola one would almost think that copulation takes place, for the 



