\V. A, 11ASWE1;L. 
4^?a 
the occluding septum from reaching the exterior, i. e. the 
space between the embryo and the shell. 
VIII. Development of the Epidermis. 
In the integumentai-y system of Temnocephala the most 
characteristic feature is the presence of a well-developed 
nucleated epidermal layer of a syncytial character. In the 
embryo this is not represented by any definite primordium, 
such as has been observed to be formed in Polyclads (Lang 
and others) and Rhabdocoeles (Caullery and Mesnil [4], 
Breslau [3]), and there is no process corresponding to the 
process of overgrowing of the embryo by an epidermal layer, 
such as occurs in these groups. When an epidermis is first 
disceimible, it consists of a very thin membi-ane with wide- 
apart flattened nuclei, covering only the ventral surface, and 
there is no evidence of any process of proliferation such as 
must accompany the spreading of the edge of this la 3 ’er by 
cell-division. It would appear, in fact, as if the epidermis 
were formed by cells migrating to the surface and there 
becoming flattened out and united together to form the 
syncytium. 
Temnocephala fasciata, unlike T. minor and T. 
Dendyi, has no cilia on the surface in the adult, and 
I have found no trace of them at any stage in the deve- 
lopment. 
IX. Development of the Reproductive System. 
The details of this process have not yet been followed out. 
In all the species examined the male part of the reproductive 
apparatus is developed at an earlier stage than the female. 
In the later stages within the egg the penis, the vesicula 
seminalis, the vasa deferentia, and the testes are all well 
advanced. In T. fasciata each testis is represented by a 
