30 THE NAUTILUS. 



dividual be already established in some way, or becomes so only 

 with the development of the gonad. 



On the other hand, in very old specimens, the ovaries and testes 

 seem to become atrophied, and lose their capacity of producing 

 ova and sperma, respectively. There is a mass of fibrous, connec- 

 tive tissue, while the glandular elements are considerably diminished 

 or entirely lost. 



Yet it must be mentioned here that there is another cause of that 

 degeneration. In the ovaries and testes of many species and differ- 

 ent genera, from the Ohio and Tuscarawas Rivers, the Ohio canal, 

 and other places, I have found a singular, polymorphous, worm-like 

 parasite, of microscopic size and low organization, sometimes in im- 

 mense numbers. It is very common, in old and middle-aged spec- 

 imens, and wherever it occurs, the products of the gonad are con- 

 siderably diminished or entirely suppressed. Details will be found 

 in another place. 



It has been stated that in young Lampsilis the number of sacks in 

 the marsupium is considerably smaller than in older ones. In the 

 younger specimens of most other groups only a small area of the 

 outer branchia3 may be charged, and slightly so, usually about the 

 middle. The same is found in phaseolus. One specimen, 62 mill, 

 long, had 12 sacks on one side, 38 on the other ; all of them were 

 quite small, but of rather unequal sizes. 



4. Hermaphroditism, etc. It has been asserted, by different writers, 

 partly long ago, that some, if not all, of the Unionida? are herma- 

 phroditic, as some other groups of Pelecypods are. From my own 

 observations I can say that it is found occasionally, rather an ex- 

 ception than the rule, in the large majority of our species. In a 

 number of specimens, ova and sperma were found in the same gonad, 

 but usually one product was greatly in excess of the other. Very 

 probably it has been overlooked in many instances, as there maybe 

 only a few acini producing sperma in an " ovary," or vice versa. It 

 takes a very keen eye to see that unaided, and to look over every 

 parcel of a large gonad, requires an undue amount of time, when 

 scores and hundreds of specimens are to be examined. > And so it 

 would be with microscopic examination, either by looking over 

 samples from all parts of the gonad, or by section series on hardened 

 specimens. Yet the question should be studied carefully, especially 

 as to Anod. imbecillis and some other species. That would be a task 

 for persons having a good deal of time at their disposal. 



