Astrenomy. 323 



are now almost destroyed. In many sections this valuable timber 

 has entirely disappeared ; and in others the branchless trunks, 

 still standing, attest the destructive effects of this parasite. As 

 soon as a bunch of mistletoe fixes itself upon a branch, the out- 

 ward extremity ceases to grow, and finally dies. The tree soon 

 presents a clubby appearance, followed by death. A grove of 

 ity, was notable a few years ago 

 for its depth of foliage and the thrifty growth of its individuals. 

 It is now a picture of desolation. A few years will witness its 

 total destruction. The importance of this subject to the indus- 

 trial interests of the country should commend it to the attention 

 of those interested in arboriculture, in the hope that some means 

 may be devised for preventing the ravages of this parasite. 



8. M&lian »,,,! l>,r,n 1 /•'/„*.,/ * nfrlh t> n t„ tin h »t., f , f of 

 Vertebrate Limbs; by James K. Thachee.— This memoir is from 

 volume iii of the Transactions of the Connecticut Academy. It 

 U the result of a careful comparison of the fins of various species 

 of fishes at early stages of growth, and is illustrated by twelve 

 plates. The view reached is in opposition to that of Gegenbaur 

 on the subject, and is expressed thus: 



As the dorsal and anal fins were specializations of the median 

 tojda of \ i tins were specializations of the 



two lateral f,.ld.i which are supplementary to the median in com- 

 pleting the circuit of the body. These lateral folds, then, are the 

 homologues of riu- Wolllian ridges, in embryos of higher forms. 

 Here, as in the Median fins, there were formed chondroid and 

 finally cartilaginous rods. These became at least twice segmented. 

 The orad ones, with more or less concrescence proximally, were 

 prolonged ii 

 fine, and a 1 

 limb girdle. 



If now we seek to determine the form of limb for the Protogna- 

 thostomi, that is to say,fortha: time for ,. hi h the archipterygium 

 in its entirety is proposed, we should propose this : 



The limbs of the Protognathostomi consisted of a series of 

 parallel articulated cartilaginous rays. They may have coalesced 

 somewhat proximally and orad. In the ventral pair they had ex- 

 tended themselves mesiad until they had nearly or quite met and 

 formed the hip girdle. They had not here extended themselves 

 dorsal. In the pectoral limb the same state of things prevailed 

 but was carried a step further, namely, by the dorsal extension of 

 the cartilage constituting the scapular portion, thus more nearly 

 forming a ring or girdle. 



IV. Astronomy. 



1. Elements of Borelly's Comet; by Aaron N. 

 tant TJ. S. Naval Observatory. (From a letter to t 

 Washington, D. C, March 13, ]877.)-I have deduced the foUow- 

 *ng elements of Borelly's Comet from equatorial observations 

 made at this Observatory, February 9, 12 and 17. 



