28 ILLINOIS BIOLOGICAL MONOGRAPHS [28 



the developing or mature cercaria of this group. A non-nucleated epidermis 

 is shown in the process of sloughing off for the hemistome cercaria (C. 

 ptychocheihis , Fig. 54). Underneath is a distinct layer of " cuticula. " Beneath 

 the " cuticula " is a lining of transverse and longitudinal muscle fibers. Median 

 to the complexes of the longitudinal muscles are the complexes of the con- 

 nective tissue. The whole structure, from the inner wall of the "cuticula" 

 thru to the free parenchyma, is infiltrated and bound together into a single 

 mass by a mucoid secretion. This secretion is indifferent to stains. The epi- 

 thelial cells of the complex send out long processes toward the integument, so 

 that the processes penetrate into the latter. These cells suggest gland cells, 

 concerned with the secretion of the "cuticula." They are not potentially 

 different from the underlying parenchyma. 



Among the distome larvae the writer has studied the "cuticula" problem 

 for echinostomes, schistosomes, and xiphidiocercariae. The redia of C. trisole- 

 fiata possesses an ectodermal reticulum in which are found large vesicular 

 nuclei. This covering is impregnated with large granules which are indifferent 

 to stains. In the cercaria of this form (Figs. 128-133), there is an ectodermal 

 layer present, very thin, with the nuclei arising from the surface as minute 

 tuberosities. Beneath this is the thick layer of "cuticula." The epidermis 

 has been lost in the tail. No " Epithelzellen " are visible in the mesenchyme 

 complex. For the schistosome larva, C gracillima, there are definite nuclei 

 present as minute papillations rising above the surface of the epidermal layer. 

 The sporocyst of this form has no "cuticula." The body wall consists of 

 a single layer of ectoderm cells, arranged end to end, the nuclei of which are 

 oval to subspherical. In the distome, C. glandulosa, the sporocyst wall is 

 composed of a single layer of epidermal cells, with falciform nuclei. In the 

 cercaria the epidermis is present only in individuals where the tail is still 

 attached. Here nuclei are present in the peripheral layer of the body, but 

 are not found in the covering of the tail. The "cuticula" is a thin envelope 

 around the circular layer of muscles. 



The study of these trematodes with reference to the problem of the integu- 

 ment has led the writer to set aside the view that the "cuticula" is ectodermal 

 in origin, because the ectoderm is superficial, lying outside the "cuticula." 

 The impregnation of this layer with cuticular granules might lead one to be- 

 lieve that the two layers are one, but the earlier history of the layers shows 

 that this conception is erroneous. No hypodermis is found in any of the species 

 studied. Consequently the Blochmann theory can not hold for these species. 

 No special gland cells have been found to support in its entirety the theory of 

 Brandes. On the other hand the evidence of this study points to the sus- 

 taining of Leuckart's theory of the parenchymatous origin of the basement 

 membrane on the following grounds. 1) In all the species the basement mem- 

 brane arises from tissue beneath the ectodermal layer. 2) In all cases where 

 there is an ectodermal layer only (in sporocysts) , no basement membrane is 

 found. 3) The heaviest layer is found in species where the parenchyma has 

 a widely diversified potency, such as salivary, cystogenous, locomotor and 



