Habits and structure of Cotylaspis insignis Lerpy. 231 
body of the parent. In this C. insignis is quite unlike the rest of 
the known Aspidobothridae. 
The yolk-cells have distinct boundaries rendered nearly invisible 
by crowding (see Fig. 61). They are numerous and considerably 
smaller than the embryo cell (0.025 mm in diameter). They look 
quite unlike the yolk-cells of the yolk receptacle having a clear 
peripheral zone aud a denser central zone, in the center of which 
is the nucleus (Fig. 62). This contrasts strongly with the cell 
before it has become incorporated with the embryo, in which distinct 
grains of yolk are seen and located at the periphery of the cell, 
and may be an indication of the beginning of changes related to 
the nutrition of the egg-cell, or possibly they have contributed to 
the formation of the shell of the egg. 
Recently discharged eggs were kept under observation in the 
hopes of learning something about the development. Such eggs 
undergo changes, shown in Fig. 64—70, coming to a standstill at 
the end of three days. Speculations as to the cause of this do not 
lead to any satisfactory result. It we suppose it is due to non- 
fertilization, then we have difficulty of the shell, apparently imper- 
vious to a spermatozoon. If the egg is not fertilized befere it 
reaches the uterus it is then unlike the other Aspidobothrids. If 
it is fertilized in the oviduct, then it is difficult to see why it does 
not go on and develope. Possibly some temperature condition, to 
be furnished by an intermediate host, is required, or a peculiar 
chemical stimulus may be the condition needed. If it has not yet 
been fertilized then this may be a device for cross-fertilization, and 
copulation be thereby indicated. The presence of the shell would 
seem to be an insuperable objection to the latter hypothesis. A 
study of C. insignis more continuously throughout the year will no 
doubt help greatly in dealing with the problems of its life history. 
n) Anatomy of a young individual. 
In October 1900 I received specimens of Anodonta from Chautauqua 
and examining one of them with a simple microscope found a fluke 
very much younger than any that I had seen before and of sufficient 
interest to deserve a detailed description. It was examined both 
alive and after fixation (HgCl,) and sectioning. It was found on 
the surface of the visceral mass, not far distant from the kidney. 
The living animal used its ventral sucker and the mouth funnel 
in the usual manner, adhering with the latter as shown in Fig. 74, 
