newed after they open. It is probable that in 

 these cases the depression of cihary activity is due 

 primarily to the accumulation of metabolites 

 There exists, however, another type of inhibition 

 of ciliary motion that is not associated with 

 changes in the outside environment. It can be 

 observed on gills exposed by the removal of a 

 portion of the valve. The oyster is placed in a 

 suitable container supplied with slowly running- 

 sea water, and the gills are strongly illuminated 

 and examined under a dissecting microscope. 



The time required for a small inert particle 

 (carmine, or powered oyster shell) to be moved 

 along the terminal groove between the two selected 

 points in the microscope's field of view is recorded 

 with a stopwatcli. Copious discharge of mucus 

 that impedes the transport of particles along the 

 groove was avoided by adding only minute cjuan ti- 

 tles of material in suspension. Readings were 

 repeated every minute, and the degree of expansion 

 of the gill lamellae and ostia were recorded. 

 The observations lasted from 10 to 30 minutes. 

 Ciliary motion over the terminal groove of the 

 gill frequently slowed down as the adductor con- 

 tracted, but previous rhythm was resumed within 

 a few seconds after relaxation of the muscle. 

 The most spectacular were the instances of com- 

 plete cessations of ciliary motion over the surface 

 of the entire giU following strong contraction of 

 the adductor muscle and complete closure of the 

 valves. Since a portion of the shell was removed 

 the surface of the giU remained m contact with 

 fresh sea water and the cessation of ciliary activity 

 could not be attributed to the accumulation of 

 carbon dioxide or other metabolites. 



The association of the inhibition of ciliary 

 motion with the contracted state of the adductor 

 muscle is showii in table 17, which contains ex- 

 cerpts of the records of observations made on 

 two male and two female adult oysters. Tem- 

 porary depression and sometime stoppage of ciliary 

 motion were often observed after occasional 

 contractions of the gill muscles. In these cases 

 the inhibitory impulses seem to be less pronounced 

 than in the case of the contraction of the adductor 

 muscles. Electric shock applied from tlie DuBois 

 inductorium direct to the gill epithelium or to 

 the edge of the mantle liad no effect on ciliary 

 beat of the frontal and terminal cilia. Only in 

 the case of a sliock sufl^ciently strong to cause 

 contraction of the adductor muscle was there a 

 cessation of ciliary activity. 



T.\BLE 17. — Association of the velocity of ciliary current 

 along the terminal groove of the external right demibranch 

 and the state of contraction of the adductor muscle 



[Excerpts of the protocols of the four experiinenis with adult and sexually 

 mature C. virginica made in .\ugust at Woods Hole, Mass!.] 



I Readings made every minute within time shown in this column. 

 : Complete contraction. Ciliary motion stopped along the entire terminal 

 groove and on the surface of the gill. 



Extu'pation of the visceral ganglion or its burn- 

 ing witli an electric needle had no effect on ciliary 

 motion of the gill, indicating that inhibition does 

 not originate in the ganglion. The frequent 

 comcidence of the cessation of ciliary motion with 

 the contraction of the adductor muscle and the 

 subsequent resumption of ciliary activity after its 

 relaxation suggests the possibility of a neuroid 

 transmission of the inhibitory impulse which may 

 originate during muscular activity and spread 

 over the ciliated surface of the gill. 



Since the problem of the impulses causing 

 inhibition of ciliary motion has not been studied 

 sufficiently, it is impossible at this time to present 

 a reasonable explanation of this puzzlmg phenome- 

 non. 



The transport of water by the gills during feed- 

 ing and respiration is discussed in chapter IX since 

 this function is controlled jointly by the mantle and 

 adductor muscle. 



BIBLIOGRAPHY 



Alder, Joshua. 



1S51. A repl}' to some statements of Ur. Williams 

 on the controversj- respecting the branchial cur- 

 rents in the Lamellibranchiata. Annals and Mag- 

 azine of Natural Histor_v including Zoology, Botany, 

 and Geology, series 2, vol. 14, pp. 177-182. 



.4tki.\s, Daphne. 



1937. On the ciliary mechanisms and interrelation- 

 ships of lamellibranches. Part II. Sorting devices 

 on the gills. Quarterly Journal of Microscopical 

 Science, vol. 79, No. 315, pp. 339-373. 



1938. On the ciliary mechanisms and interrelation- 

 ships of lamellibranches. Part VII. Latero- 



THE GILLS 



147 



