On the reproductive system of Planaria simplissima. 459 



collected at its head close against the ovary (PL 31, Fig. 4 sp^). 

 The glands of the vagina show a slight secretion the passage of which 

 through the epithelial walls has already been described. The epi- 

 thelium of the atrium has shown no appearance of glandular activity 

 at any time. 



Worms were had in abundance up to the first of January, from 

 then until the first of April we were unable to obtain them from out 

 of doors and were obliged to rely upon those kept in the laboratory. 

 They were found in small numbers during April, but since then none 

 have been taken. The method of obtaining them was to place the 

 ooze scraped from the masonry and woodwoik on the upper side of 

 an old dam, in an aquarium jar full of water. The worms crawl out 

 upon the sides of the jar in a few days or even hours and can then 

 be easily collected. Placing the jars in a warm room and in a dark 

 closet failed to bring them out, so that it is not likely they remained 

 hidden in the ooze during the time we were unable to obtain them. 



III. Structure of the Muscle Fibres. 



The only point which will be discussed under this head is the 

 occurrence in the fibres of the main longitudinal system of certain 

 dark areas, which I shall describe carefully but for which I am un- 

 able to give a satisfactory explanation. Three layers of muscle fibres 

 are present just below the basement membrane: 1) a circular layer 

 of fine fibres, 2) a layer of diagonal fibres slightly larger and crossing 

 at the sides of the body as well as at the mid-line and 3) the main 

 longitudinal consisting of the large cylindrical fibres shown on PI. 32, 

 Fig. 12. There is no ditîerentiation apparent in the circular and 

 diagonal muscles which is in accord with the observation of Lang ('81), 

 IjiMA ('84, p. 381) and Woodworth ('91, p. 22). These authors have, 

 however, recorded in the substance of the longitudinal fibres a differ- 

 entiation into "Rindenschicht" and a "Marksubstanz". Chichkoff ('92, 

 p. 480) has described the fibres of the first two layers originating 

 from a bipolar cell which grows at one end and shows (tab. 15, 

 Fig. 10 a) fibres with a terminal enlargement, the nucleus. His sta- 

 tement of the subsequent history is that "plus tard cette fibre large 

 et simple se divise en plusieurs (tab. 15, fig. 10 h and c) et cette 

 division entraîne la disparition du noyau". The final condition there- 

 fore is what the others describe. He has shown (figs. 18 and 19 nm) 

 the large fibres of the longitudinal system each with a single nucleus 

 appearing as an enlargement near the middle of its length and sup- 



