Febsuaky 2, 1900.] 



SCIENGE. 



171 



angle, the distal ends being directed down- 

 ward in both cases. Thus there is seen to 

 be a striking analogy, if not homology, be- 

 tween bud and basal polyp. The forma- 

 tion of supernumerary tentacles and other 

 structures is common in this species, so it 

 may be possible to regard the bud as a 

 supernumerary and precociously developed 

 basal polyp. 



Notes oil the anatomy of Acmcea testudinalis, 

 Milller: M. A. Wilcox. 

 The following points were made : 



1. There is probable, though not conclu- 

 sive evidence in favor of a winter migration 

 to deeper water. 



2. The inner face of the mantle is uni- 

 formly clothed with cilia borne, not contin- 

 uously, but in patches some 20-30 /j. apart. 



3. Subepidermal glands are situated at 

 the mantle margin. Unlike those described 

 by Haller in a similar position, they are 

 unicellular. Whether they contribute to 

 the formation of the shell is uncertain. 



4. The inner face of the mantle also bears 

 subepidermal glands which are scattered 

 and are probably unicellular mucous glands. 



5. Animals killed by agents which pro- 

 duce strong contraction, exhibit folds of the 

 mantle which lie parallel to the foot and 

 contain blood spaces. These seem entirely 

 similar to those described by Haller in 

 Lottia (^acmcea) ■punctata but in A. testudinalis 

 are artefacts. 



6. Both mantle tentacles and those borne 

 on the head are richly provided with sense 

 cells of Flemming. 



7. The cephalic tentacles have each a 

 large axial cavity which communicates with 

 the cavity of the head. The wall surround- 

 ing the tentacular cavity consists of con- 

 nective tissue in which longitudinal muscle 

 fibres are imbedded and the tentacle, there- 

 fore, is intermediate between the ordinary 

 solid prosobranch tentacle and the invagin- 

 able tentacle of the stylommatopbora. 



8. The chief nephridium closely resembles 

 that of Patella, except that the portion which 

 lies on the left side in A. testudinalis extends 

 forward to the pericardium and probably 

 communicates with it. The greater portion 

 of this nephridium corresponds to what 

 Haller describes as part of a coelom. 



Locomotion in Solenomya and its relatives. G. 



A. Deew. 



These forms burrow rapidly in mud or 

 sand. The extremity of the foot is pro- 

 vided with two muscular flaps that may lie 

 side by side or be spread apart. When the 

 flaps lie side by side the extremity of the 

 foot is wedge shaped, and the foot can 

 easily be thrust into mud or sand. When 

 the flaps are spread apart they form a very 

 effective anchor. With the foot thrust into 

 the mud and the flaps spread, a contraction 

 of the retractor foot-muscles results in draw- 

 ing the shell into the mud up to the posi- 

 tion of the spread flaps. From this position 

 another thrust can be made. 



Beside burrowing, Solenomya swims quite 

 rapidly. The thick elastic cuticle extends 

 past the calcareous portion of the shell, 

 along its ventral borders to a distance 

 fully equal to one-fourth the entire width 

 of the shell. The margins of the mantle 

 have united ventrally, leaving a small pos- 

 terior opening through which water can 

 be forced, and a larger anterior opening 

 through which the foot can be protruded. 

 The region of the united margins of the 

 mantle is occupied by a rather broad longi- 

 tudinal muscle that spreads out around the 

 anterior and posterior openings to form 

 sphincters. The radial pallial muscles are 

 also strongly developed. These extend 

 from the calcareous margins of the shell to 

 the free margins of the cuticle. 



When the foot is protruded nearly to its 

 full extent, and the pallial muscles are re- 

 laxed, the anterior opening is much larger 

 than the foot, and through it water can 



