NOTES ON BRANCHJOBDELLA. 103 



sperm. The parts of the sperm and their derivation are sum- 

 marized in the following words : " Der Samenkorper besteht also 

 jetzt (Fig. 132): (i) aus dem nebenkern, (2) dem von einer 

 di'mnen Membran gebildeten Schlauch, (3) dem asu dem Kern 

 hervorgegangenen konischen Teil, (4) dem Verbindungsstuck, 

 welches aus dem protplasma der Zelle anstand und aus welchem, 

 (5) der Schwanzfaden hervorgesprosst ist," page 328. 



Moore, '95, describes the morphology and histology of Bdcllo- 

 drilns\\\ detail, a form which was first described as Branchiobdella, 

 and the agreement of B. instabilia is so close that a separate 

 description is not warranted. In connection with the description 

 of the reproductive system the following statement is made : 

 "The first steps in the development of spermatozoa begin before 

 the worm has nearly reached full size, and proceeds continuously ; 

 the various stages floating freely in the ccelom. in which they 

 complete their development. In the mature worm the cavities 

 of the fifth and sixth post-cephalic somites are filled with sper- 

 matozoa in various stages of development, while the testes 

 proper have become much reduced and inconspicuous. The 

 details of this process have been admirably worked out and 

 described by Voigt ; and it need only be added that what obser- 

 vations the writer has made are in accordance with his account" 

 (page 519). In the same year Calkins' paper appeared on the 

 spermatogenesis of Lnmbricns and makes no mention of the 

 works of Voigt. 



The ovaries are located in the seventh post-cephalic somite 

 and consist of two separate sacs, one 'on each side of the digestive 

 tube. The young ova in one half of the ovary may be in a state 

 of division while the rest of the ova are in the resting state. This 

 division is by the usual indirect process with no evidence of astral 

 fibers. A distinct centrosome is present at each pole of the 

 spindle, the spindle fibers arising from within the nucleus. The 

 chromatin assumes the characteristic spireme state preceding the 

 formation of the equatorial plate. An early prophase stage in 

 the division of an ovum is shown in Fig. 5. Voigt figures ova 

 having two nucleoli and believes that this is an indication of ami- 

 totic division. My sections have been studied with this particular 

 point in mind and no case of amitosis has been noted. In a few 



