SIGNIFICANCE OF LARVAL MANTLE OF FRESH-WATER MUSSELS. 
211 
With the larvae of the Anodontas, as brought out by the foregoing discussion, 
development during parasitism is characterized by the following features, to which 
attention is directed. 
There occurs, first, a complete destruction of host tissue inclosed within the 
valves, with the initiation of an intracellular nutrition by means of the pseudopodial 
ability of the transformed mantle, which very early tends to lose its cell distinctions 
and fuse together. Following this there occurs the appearance of the definitive 
mantle through whose development the mushroom stage of the larval mantle 
arises, which is considered to be a relatively functionless organ, with endosmotic 
nutrition apparently centered on the cells of the definitive mantle; and, finally, 
there is the complete absorption of the mushroom body, coincident with the com- 
pletion of the definitive mantle, which marks the end of the parasitic period. 
Of all the many unionids the development of the hooked larva of Anodonta 
alone has been studied closely, yet when one considers the great number of forms of 
naiads, the diversity in their structure, and the lack of complete uniformity in 
manner of metamorphosis from the glochidium to the juvenile stage — some species 
developing without parasitism — it is perhaps not surprising to find a digression 
from the Anodonta type in the larval development of Lampsilis luteola. 
METAMORPHOSIS OF LAMPSILIS LUTEOLA. 
In the course of experimental field propagation of this mussel during the sum- 
mer of 1921 at Lake Pepin, Minn., larval mussels were collected from experimental 
pen bottoms shortly after they were shed from their host fish. The examination 
of the material thus collected brought tc^ light the unexpected presence of primitive 
mantle cells. In addition these cells exhibited differences in structure and function 
from the mantle cell conditions of Anodonta. This, prompting a study of the earlier 
parasitic development, led to the discovery of the retention of the individual larval 
mantle cells without fusion until the end of parasitism, they having apparently 
a nutritional function throughout. This has been determined to‘ be a normal 
condition by series of sections at different stages of development. The author has 
sectioned about 100 encysted individuals 2 of parasitic larvse and about 50 of free 
larvae after the completion of metamorphosis, so that the different stages of develop- 
ment have been determined with certainty. 
The only similar studies having been on several European and a single American 
species of Anodonta, it was considered desirable to obtain further data on another 
American Anodonta, both for comparison with former observations and for the 
purpose of thoroughly familiarizing the author with the material published. With 
this in mind preparations of the larvse of Anodonta corpulenta on Lepomis humilis 
were made and studied. 
The sections of glochidia of Lampsilis luteola were used as type forms in the 
illustrations in view of the gross similarity in cell structure of both the hooked and 
hookless glochidia. The only differences that do occur are concerned with the pres- 
ence of the larval thread in the former and a lack of similarity in sensory cell con- 
ditions; otherwise the embryonic structures are of the same order, although the 
» Part of this material was obtained from H. W. Clark. 
