ECOLOGY OF ISLE ROYALE. 249 



ANNOTATIONS ON CERTAIN ISLE ROYALE INVERTEBRATES. 



nn. CHAS. C. ADAMS. 



The following annotated list of Isle Royale invertebrates includes the 

 groups which have not been made the basis for separate papers by 

 specialists. For the determination of these I am indebted to the follow- 

 ing persons : Prof. N. A. Harvey, the Sponge ; Dr. T. H. Montgomery, 

 Hair-worms; Prof. Frank Smith, Earthworms; Dr. J. Percy Moore, 

 Leeches; Miss Ada Weckel, Amphipods; Dr. Harriet Richardson, Sow- 

 bug; Mr. Nathan Banks and Mr. J. H. Emerton, Spiders; Dr. J. W. 

 Folsom, Spring-tail; Mr. E. B. Williamson, Dragonflies; Prof. Herbert 

 Osborn and Mr. J. B. de la Torre Bueno, Hemiptera; and to Prof. A. J. 

 Snyder and Dr. James Fletcher, Lepidoptera. 



In general, in addition to the field notes Avhich include those made 

 by Dr. H. A. Gleason and myself, the geographic range has been outlined 

 and a selected series of references is given for the convenience of the 

 student of the Michigan fauna. The insects were largelj^ collected by 

 Dr. Gleason, the writer, and B. F. Savery who collected insects about 

 the camps, but all members of the party aided in the collection of the 

 specimens. The field numbers are indicated in parentheses, preceded by 

 G in the case of Dr. Gleason's numbers and A in my own. 



An examination of these lists will reveal their incomplete. character, 

 as an effort was made to make representative rather than complete col- 

 lections of the groups. On account of the small amount of zoological 

 information which we possess from Isle Royale it has been thought desir- 

 able to make the determinations of the collections as complete as cir- 

 cumstances would allow. 



POEIFERA. 



Spongillidae. 



Spongilla lacustris (Linn.). Fresh Water Sponge. A small colony 

 of this sponge was found on July 26 in shallow water near the head of 

 Rock Harbor (III, 3) by Gleason. Prof. N. A. Harvey examined the 

 specimen and makes the following comments: "Small encrusting sponge, 

 with a tendency to branch. One branch cylindrical, full of gemmules. 

 Skeleton spicules smooth, pointed, slightly curved, numerous. Dermal 

 spicules, few, half as long as skeleton spicules, densely spined, spines 

 short, more numerous towards the ends, slightly curved. Gemmiiles 

 with very thin membrane, destitute of spicules, foramen oval. 



"This sponge is evidently a weak form of Spongilla lacustris (Linn.). 

 It is very close to the paupercitla of Bowerbank. There can be no 

 question about the identity of this sponge, although it is somewhat un- 

 usual to find gemmules so well developed in July. It developes its 

 gemmules ordinarily very late in the fall. The spicules on the gemmule 

 appear to be wholly wanting, and the dermal spicules are not numerous. 

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