177 



this connection. It also appears tliat the descriptions of penial bulbs 

 which have appeared in the literature since 1905 agree with the defini- 

 tion of the lumbricillid tyi)e. Thus far no deviation from this type 

 is known to occur in the genus. 



The characteristics of the enchytra^id type of penial bulb as de- 

 scribed by Eisen have already been given. In defining the subfamily 

 Encliytrccincc ("05, p. 61) he makes the following statement concern- 

 ing the penial bulb: "In this family the penial glandular structures 

 are not confined within a single bulb as in Lumbricillinse, but are broken 

 up in two or more masses of papillse, often of unequal size. In a 

 cross-section of the body these papillre may be seen to extend from the 

 median line to the other side of the spermiducal pore, and even in the 

 long diameter of the body tlie glands have a more or less considerable 

 extension. In some species these glands are situated close to each 

 other, in others again they are separated by the common tissue of the 

 body-wall." According to Eisen two genera, Bnchytrccus and Michael- 

 sena, are characterized by this type of penial bulb. In defining the 

 genus Enchytrccus Eisen makes the following statement: "No single 

 penial bulb, but one or more isolated glandular papillos situated in the 

 vicinity of the spermiducal pores, generally and principally ventral 

 to the pores. Numerous transverse muscles connect the ventral and 

 lateral parietes surrounding the spermiducal pores." 



The studies made by the writer on the genus Bncliytrcuns show 

 that Eisen's diagnosis can not be used safely in distinguishing it. B. 

 gillettensis conforms in no respect to the type of penial structure which 

 Eisen claims to be uniform for the genus, but has instead a single 

 compact glandular bulb in which the muscular investment does not 

 penetrate into the interior. No penial structures are present outside 

 of the bulb, and the sperm duct penetrates the bulb. In fact, it is a 

 typical lumbricillid bulb. Stephenson ('11, p. 50, pi. XLVIII, fig. 

 10) describes and figures the penial structure in B. nodosus, which, 

 also, is of the lumbricillid type. It appears that at least two species 

 of the genus are radically different in the structure of the penial bulb 

 from the enchytraeid type as defined by Eisen. The writer has also 

 studied the penial structure in sections of B. alhidus, made from 

 specimens collected at Woods Hole, Massachusetts, by Professor Frank 

 Smith. Alichaelsen ('86b, p. 39, pi. II, fig. 3) described and figured 

 the structure of the penial bulb in B. mobii, which has been shown 

 to be a synonym of B. alhidus. The specimens from Massachusetts 

 have penial bulbs which correspond exactly to the description given by 

 Michaelsen. However, the structure of the bulb in B. alhidus does 

 not conform entirely to the enchytr?eid type of bulb. It is broken up 



