Life-history aud Anatomy of the Appendiculate Distomes. 375 



the ganglia and nerves is filled with fine fibrillae. Ganglion-cells are 

 present in greatest number in the ganglia and the conamissure, but 

 are also present in the nerves; they have always a peripheral position. 

 I have not observed the finer nerves of the animal. 



The Sexual Organs. 



The structure of these organs in the worm under discussion is 

 identical in most respects with that of the adult Apohlema appendi- 

 culatum as described and figured by Wagner (1860), Juel (1890), and 

 MONTICELLI (1891). 



The female organs. These organs were not fully mature. 

 The ovary is an oval body with a diameter of 0.03 mm (PI. 25, Figs. 2 

 and 3, ov.); the two vitelline glands are compact, oval, bodies, each 

 with an average diameter of 0.037 mm (PI. 25, Figs. 2 and 3, vit. gl) : 

 these three glands form a closely approximated group lying near the 

 middle point of the body and somewhat towards the ventral side. The 

 ovary lies in front of the other two glands. The vitelline ducts and 

 the oviduct are extremely short and lead to a common point or "Central- 

 raum" between the glands from which they spring; from this point the 

 uterus emerges. I could detect no receptaculum seminis or Laukeu's 

 canal; the latter organ has not been observed in any member of the 

 genus Apohlema; the absence of the receptaculum seminis, which Juel 

 (1. c.) describes in the adult A. excisum and A. appendiculatuni, is 

 probably due to the youth of the animal. The shell-gland is also ab- 

 sent, but is probably indicated by a few scattered cells which are 

 occasionally to be seen in the neighborhood of the "Centralraum". 



The uterus (which is not shown in the figures) is a narrow canal 

 with a diameter of 0.0016 mm and extremely thin and delicate walls. 

 It never contained eggs. It passes from the "Centralraum" with many 

 twists and turns first to the hinder end of the body, it then changes 

 its direction and passes forward with a somewhat straiter course to the 

 region of the acetabulum; here it was lost and could not be traced 

 farther, either in the live worm or in sections. I have, thus, not ob- 

 served the anterior end of the uterus, and believe that in the worms 

 I studied it had not yet developed. The observations of Juel (1. c. 

 p. 26) and others on the adult worm show that the anterior end of 

 the uterus, in company with the ejaculatory duct, joins the inner end 

 of the genital vestibule. 



The male organs. In sharp contrast to the immature condition 

 of the female genital organs, the male organs appear to be fully formed 



