AND THE CLASSIFICATION OF WORMS. 5 



of the parenchym of Amphilina with what Walter and myself have found in other Trema- 

 tods. Blumberg 1 agrees with Leuckart, while Schneider 2 gives a singular interpretation 

 to the histological appearance of the parenchym, which seems to me quite unwarrantable. 



The curious cords of fine trabecule, forming a meshwork, and to which the Germans 

 have applied the name of Balkenstr tinge, are known to exist in a variety of Planarians 

 and Cestods, and Salensky describes them in Amphilina, but I cannot discover anything 

 like them in Distomum crassicolle nor D. hepaticum. 



The true water vascular system (fig. 1, W.v.) may, however, be very easily seen ; in part, 

 at least. There is only one main stem, which is enormously large. It begins at the hind 

 end of the animal, where it opens externally, and enlarging very quickly (fig. 7) it runs 

 straight forward (fig. 1, W.v.) close underneath the back, its diameter gradually diminish- 

 ing, reaching half the length of the body. I have not seen any branches or canals con- 

 nected with it. One might perhaps easily discover them with the help of injections, which 

 I hope to try at some future time. In my series of longitudinal sections, there are several 

 in which the wall of vascular sac is cut parallel to its surface. In these cases there are a 

 number of pale nuclei visible. They are themselves of unequal size (fig. 8), but are much 

 larger than any other nuclei in the body of the worm. They are at irregular distances 

 from one another, and though they probably form part of a pavement epithelium, yet I 

 could not trace any indication of intercellular lines, or of cell membranes around them. 

 But the characteristic feature in the lining of the main sac is the presence of innumerable 

 small, highly refractile granules, nearly spherical in shape, and yellowish in color (fig. 8). 

 They are of various sizes, irregularly distributed, but apparently never touching one an- 

 other. I can surmise nothing as to their nature. They appear with equal distinctness in 

 transverse sections, and lie within the membrane upon which the Intima rests. This may 

 be considered a basement membrane ; it has a fibrous structure and is colored by carmine. 



I agree with Walter (I. c.) in considering the spaces in the parenchym to be connected 

 with the water vascular system. In Distomum hepaticum I have seen branches pass off 

 from the main stem and connect directly with the lacunae of the parenchym, but my 

 attempts to repeat this observation on D. crassicolle have hitherto been unsuccessful. 



Among the dermal muscles, and immediately underneath the so-called " cuticula," are 

 pear-shaped cells, with large circular or oval nuclei, which are usually not uniformly 

 stained, and contain distinct nucleoli. These are probably unicellular glands, at all events 

 they are, as is proven by their position and histological character, the homologues of the 

 layer of gland, cells which underlies the basement membrane in Cestods and Pliaryngocoela. 

 I have seen them in various Trematods, and they probably exist in all flat worms. But in 

 Trematods and Cestods they are less developed than in the Planarians, showing the close 

 relationship of the two parasitic orders. 



The oral sucker may be best described in connection with the digestive apparatus. The 

 ventral sucker (fig. 7, S) is a small circular disc, whose vertical diameter is about one-third 

 of the width of the disc (fig. 11, S, longitudinal section). It is composed mainly of ver- 



1 Blumberg. Ueber den Bau des Arapliistoma conicum. 2 Schneider. Untersuchungen iiber PlaUhclminthen. 1873. 



Inaug. Diss. Dorpat, 1871. p. 12-15. 



