GLOCHIDIA — FACTOES UNDERLYING ENCYSTMENT 469 



trary, that glochidia may be spawned in the absence of fish is 

 abundantly proved by laboratory observations on mussels held for 

 experimental propagative purposes. Moreover, there is no reason 

 to doubt that expelled glochidia retain for some time their ability 

 to gain attachment, and hence immediate infection is not im- 

 perative. Lefevre and Curtis ('12) mention having kept free 

 Strophitus glochidia alive for two or three weeks. It, however, 

 does not follow that the larvae are in a favorable physiological 

 condition throughout a correspondingly long period; experience 

 in mussel propagation teaches that good artificial infections are 

 most easUy secured within twelve or more hours after removal 

 of the glochidia from the marsupium, yet there is evidence that 

 the fastest infections give inferior yields of young mussels (Dr. H. 

 R. Reuling, private communication). 



Exactly what the stimulus may be that induces a mussel to 

 spawn is undetermined. It is interesting to note that such a form 

 as Lampsilis ligamentina holds glochidia as long as eight months 

 before liberating them. During this period the larvae are per- 

 fectly satisfactory if removed by operation and used for infection 

 purposes. What impels the gravid female eventually to rid 

 itself of larvae awaits explanation. 



or anodonta and eggs are deposited between the branchial lamellae; Cuenot ('98) 

 even has a figure showing the ovipositor inserted in the exhalent siphon of the 

 mollusc, "pendant dans les orifices siphonaux!" The male Rhodeus, after 

 interesting maneuvers about the mussel, emits seminal fluid near the siphon; 

 the spermatozoa are drawn in through the inhalent siphon, are carried by 

 ciliary currents to the eggs and fertilize them. Development proceeds among 

 the gills for a period of a month, when the fry, now 10 to 11 mm. long, leave their 

 host. Olt states that the breeding seasons of the mussels and fish coincide, and 

 this he believes affords an opportunity for the expelled glochidia to encyst 

 on the fish, brought close by their peculiar breeding habits. Such reciprocal 

 behavior has been stated as a fact by Bridge ('05) and Mitchell ('11). There is, 

 however, nothing in Olt's account to indicate that this possibility was more 

 than an ingenious speculation on his part; Bridge and Mitchell offer no evidence 

 to support their statement, which is doubtless an inference, following Olt. It 

 is conceivable that investigation might prove this relation correct, yet with 

 our recent knowledge of the restriction of parasitism to definite fish hosts it is 

 not as obvious an assumption as in Olt's time; nevertheless, there is clearly no 

 reason for believing that the immediate presence of these fish in any way induces 

 or influences the actual spawning of glochidia. 



