48 



Atrium and Penis. — Vejdovsky (1895) describes and figures 

 the atrium and penis of L. variegatus. Hesse did not at first 

 ( 1894) recognize the presence of thepenis, but later (1902) reex- 

 amined his preparations and found it to be present. Wenig 

 confirmed the observations of Vejdovsky. In my former de- 

 scription of L. inconstant the following statement occurs: 

 "Whether or not a definite penis is developed I am unable to 

 state." A reexamination of my specimens has revealed the 

 presence of a penis, formerly overlooked because of its great 

 transparency. This organ and the atrium are both very simi- 

 lar to those of L. variegatus. 



Besides these more important characters in which L. incon- 

 stans resembles L. variegatus much more closely than it does 

 the species of Trichodrilus, there are others of less importance, 

 but nevertheless significant, in which the two former species are 

 closely similar. (1) They are both greenish anteriorly. (2) 

 The usual number of somites in each is more than double the 

 number in the two species of Trichodrilus. (3) They are no- 

 ticeably similar in the extreme infrequency with which sexu- 

 ally mature specimens are found. I have examined hundreds 

 of specimens of L. inconstans, taken at various times of the 

 year, and have found but three with reproductive organs de- 

 veloped. (4) The form of the brain is quite similar in the two 

 species of Lumbriculus and quite different from that of Tricho- 

 drilus pragensis as described and figured by Vejdovsky (1876). 

 (5) In both species of Lumbriculus nephridia are found in the 

 same somite as are the genital ducts, which is not the case in 

 Trichodrilus. (6) The sperm-sacs in both species of Lumbricu- 

 lus extend posteriorly from the atrial somite through a consid- 

 erable number of somites, while in Trichodrilus pragensis sperm- 

 sacs are apparently formed anterior to the atrial segment as 

 well as posterior to it (Vejdovsky, 1876, p. 548, Fig. 2 |. 



If we follow somewhat closely the general type of generic 

 and specific definitions adopted by Michaelsen (1900), we may 

 define Lumbriculus and its two species in the following terms. 



