ZOOLOGY. ■ 613 



" 1. The mouth in the larval oyster is nearly ventral in position, while 

 in the adult it opens more nearly in thedirection of the hinge or towards 

 the antero-dorsal region. 



" 2. The retractor muscles of the velum probably atrophy at the end of 

 the larval period; if they are to be regarded as the musculature of the 

 primitive mantle organ, they are replaced in the spat and adult by the 

 radiating and marginal pallia! muscles. 



"3. The intestine of the larva is a simple tubular organ ; in the spat it 

 has an internal ridge developed on one side, which tiiially becomes a 

 pronounced induplicature in the intestine of the adult. 



" 4. The anterior adductor muscle of the larva is replaced by a per- 

 manent posterior adductor in the spat and adult. (Onxley.) 



" 5. The heart and gills are wanting in the larva ; they are developed 

 as post-larval organs. The gills are at first represented by only two 

 folds ; the outer pair are developed later, and apparently from before, 

 backwards, or dorso-veutrally. 



" G. The connective tissue of the spat and adult, including the organs 

 derived therefrom, seems to be almost entirely developed during post- 

 larval life. 



" 7. The blastocoel is mostly obliterated by the development of the 

 connective tissues. 



" 8. The liver is represented by a pair of diverticula which grow out 

 laterally from the walls of the stomach of the larva ; its subsequent 

 development and subdivision into a vast number of follicles is accom- 

 plished during post-larval life. 



"9. SoQie time after fixation the larval oysterseems to lose the straight 

 hinge border of its valves, which then acquire umbones; the valves 

 retain their symmetry up to the time when the spat shell begins to be 

 formed, and it is probable that most of the larval characters of the 

 animal have disappeared when the formation of the spat shell begins ; 

 in other words, the veliger stage is past and is at once replaced by a 

 structual condition of the soft parts which approximates that observed 

 in the adult." {Ann. Eep. Com. Full.., for 1883, pp. 770-7'Jl, 1884.) 



A remarlcahle new Type of Molluslcs. — All the acephalous mollusks 

 hitherto known have distinct external valves on each side, although in 

 some, such as in the ship-worras (Teredinids) and the watering pot 

 shells (Aspergillids), the valves are extremely reduced; but in a lorm 

 recently obtained from California, external valves are not at all ap- 

 parent. When living, the animal is apparently of the "shajjc of a small 

 globose Cyprcca [or cowrie] of inflated ovoid form, and being translucent, 

 jelly-like, dotted above with small rounded papilhp, which ajipear of an 

 opaque white on the general translucent ground." "When fret^li, accord- 

 ing to the discoverer of the siteciniens, Mr. C. It. Orcutt, the animal was 

 "over an inch in length," but the contraction in alcohol is such that the 

 specimens, when received by Mr. C. II. Dall, were reduced to "less than 

 half an inch in length." 



