392 T. B. ROSSETER ON IIOLOSTOMUM EXCISUM. 



Figs. 3 and 4. Farther developments of the same. In these 

 specimens no trace can be discerned of the anlage of 

 the hermaphroditic genitalia. The looped intestine 

 can be traced some distance down from the mouth- 

 sucker into the posterior or body portion of the 

 creature, also the terminative excretory pore. x 45. 



Figs. 5, 6, 7, and 9. These illustrate the progressive advancement 

 in the perfection of the sexually mature Holostomum. 

 Of the female genitalia, only the vitellaria is plainly 

 visible. In consequence of the pigmentary character 

 of the glandular corpuscles, which are closely aggre- 

 gated, the other organs of generation are in a great 

 measure obscured. x 45. 



Fig. 8. A dorsal view of Fig. 6. x 45. 



Fig. 10. Sexually mature creature. X 45. 



Figs. 11, 12, and 13. Prepared specimens of Holostomum excisum, 

 von Linstow, 1906, and Fig. 14 is a young specimen 

 of Fig. 13. In this young Holostomum the pore of the 

 laurer canal can be defined, also some of the ducts of 

 the developing genitalia. x 45. 



Fig. 15. Caudal end of specimen, showing the deposition of ova 

 through the uterine papillus. x 45. 



Fig. 16. Laurer canal with spermatozoa in the pore. From 

 compressed specimen, the pressure causing the vesicula 

 seminalis to be ruptured, leaving one broken end 

 in the pore. x 220. 



Fig. 17. Young form of Tetracotyla tt/pica, after von Linstow. 



Abbreviations as follows : — e.p. excretory pore; g.p. genital 

 papilla ; l.c. laurer canal ; M. mouth ; o. ovary ; p.l.c. pore of 

 laurer canal ; R.s. receptaculum seminis ; s.G. shell gland ; Sp. 

 sperm ; s.s. side suckers ; t. testes ; u. uterus ; u.a. uterine aper- 

 ture ; v.s. (in Figs. 2, 3, and 4) ventral sucker; v.s. (in Fig. 10) 

 vesicula seminalis ; v. vitellaria ; y.g. yelk gland ; y.r. yelk 

 reservoir. 



Journ. Queketl Microscopical Club, Ser. 2, Vol. X,, No. 64, April 1909. 



