No. 516] THE CUTICULA OF C EST ODES 71? 



homologous to the hypodermis of other invertebrates. In 

 trematodes this moulting may occur in each of the larval 

 stages. It has been directly observed in the miracidium 

 many times, among others by both Thomas (1883) and 

 Leuckart (1886) who saw the miracidium of Fasciola 

 hepatica shed its ciliated ectoderm when it entered the 

 liver of Lymncea trunculata. In the redia and cercaria 

 stages it has also been directly observed by a number of 

 investigators. Looss has made the most complete record 

 of his observations. He (1892, 1893, 1894, also Braun, 

 1893, p. 818) has seen both the redia and cercaria shed 

 its outer epithelium in about a dozen species of distomes, 

 as just remarked, after which procedure the young worm 

 was covered with the definitive cuticula. This Looss con- 

 siders the product of secretions of the entire body of the 

 parenchyma. 



Although the cercaria has thus been seen to shed its 

 peripheral epithelium, there have been recorded a num- 

 ber of cases where it is not shed all at one time, portions 

 remaining until the cercaria is fully grown or nearly so. 

 The appendiculate distome I described some time ago 

 (1898) was a good example of this procedure. The ap- 

 pendix of the young worm in this case retained its cer- 

 carian ectoderm although the male genital organs were 

 mature and spermatozoa were being produced. The re- 

 mainder of the body was without an epithelium, but was 

 covered by the characteristic cuticula, which was also 

 present beneath the epithelium on the appendix. This 

 epithelium was soon after moulted and then the outer 

 covering of the appendix was exactly similar to that of 

 the rest of the body. 



In cestodes the early stages of development are very 

 similar to those of trematodes, the ectoderm having been 

 observed by Schauinsland (1885), Leuckart (1886) and 

 others to be moulted in exactly the same way. It is the 

 opinion of many students of cestodes, however, that the 

 stage in which an outer epithelium is present is passed 

 over in most of these animals. The young worms thus 



