DEVELOPMENT OF THE GENERATIVE ORGANS. 721 
Judging from the above description, it appears that the 
intracellular development of germs is a widely-spread pheno- 
menon, and that germ-ova originate by true endogenous cell- 
formation; and this view is still further borne out by the 
endogenous development of spermatozoa. 
Later authors have rather confined their observations to the 
manner in which the nuclei multiply; but I think it is clear 
that the continuous layer of protoplasm in which the germ- 
ova develop is, as Van Beneden suggests, either a single cell 
with many nuclei, or consists of a group of cells, the individual 
limits of which have not been distinctly observed—probably 
the result of the processes employed for their preservation. 
k. Some General Remarks on the Similarity of the Generative 
Function in Insects and Trematodes. 
Although the Trematoda are always hermaphrodite, and 
the Insecta are invariably unisexual, there is a remarkable 
similarity in the general disposition of the female generative 
organs of the two groups, especially when the generative 
organs of the highest Trematodes, the Rhabdoccelian Turbel- 
laria, and Insecta are compared. 
The diagrammatic representation of these organs in a Rhab- 
doceelian (see next page) would serve as a representation of 
the same organs in a female Insect. In both cases there is a 
bursa and a receptaculum seminis, or spermatheca; in both 
the vitelline glands apparently correspond with the testes of 
the male; and in both, if I am right in my conclusions, there 
is a distinct germ-gland. Moreover, the germ-gland in the 
Turbellarian is very similar to the parovarium of the 
Insect. 
There are, of course, points of dissimilarity, the most im- 
portant of which is the structure of the vitellogenous gland. 
This in the Turbellarian is an ordinary racemose gland, the 
ducts and follicles of which are continuous; but this condition 
is by no means uncommon in the Arthropoda, and is the form 
usually ascribed to the ovaries of Insects. 
