20 Prof. H. J. Clark on Lucemaria. 



upon the approximation of the bunches of tentacles, i^vo and 

 two, are entirely erroneous, as this obtains in all octagonal 

 Lucernarians in a greater or less degree. As these animals are 

 very sensitive and irritable, they contract upon the least disturb- 

 ance ; and as the muscular system is most highly developed in 

 the region which lies about the four partitions of the disk, it is 

 most natural that, when the creature contracts, it should draw 

 the two halves of the genitalia and the bunches of tentacles to- 

 gether more closely here than at the alternate quarters ; hence 

 arises the frequently observed quadrate outline of the disk. 

 Again, in regard to another feature oftentimes employed to dis- 

 criminate between different species, or even groups, I would say 

 that the absence of auricles alone, without other differences in 

 the animal, does not indicate a specific difference froni those 

 individuals possessing them, but rather an accidental atrophy of 

 these organs, — and that this fact is to be classed in the same 

 category as the occasional development of one of the tentacles 

 into a semiauricular body. I have .always noticed that indivi- 

 duals in such a condition have an unnatural appearance — that 

 they are not so lively as the others, and appear to be diseased*. 

 I believe this species to be identical with L. auriculaf of the 

 English coast. The most characteristic figure that I know of, 

 although unsatisfactory, is in Gosse^s little book, ' The Aqua- 

 rium'|. 



In order to contrast the structure of Lucernaria with that of 



* I have found such specimens most frequent at that time of the year 

 which is the breeding-season of our common shore-crab, Cancer {Platy- 

 carciims) irroratus, when it comes up out of deeper water, and is most 

 abundant and active. At first, onl}' now and then, I found a Lucernarian 

 with one or two auricles bitten off; but hiter it was common to find speci- 

 mens with all the auricles nipped, and nothing but a small portion of their 

 base, or a mere scar, left to indicate their former presence. The moment 

 a Lucernarian is touched by a C'-ab, it jerks its tufts of tentacles inward, 

 but the reverted auricles are left ex])osed, and all the more prominent by 

 the act than usual, and a conspicuous morsel for the predaceous creature. 

 As the season advances towards summer, the bunches of tentacles also 

 disap])ear one after another, vmtil it becomes quite common also to find 

 individuals with two, three, or four bunches bitten off; and at the same 

 time specimens become more and more rare (at the last of June, for in- 

 stance), and finally (by the early part of July) it is impossible, by the most 

 diligent search, to find a single specimen. As this happens at the time 

 when the Lucernarians are laying their eggs, it is clear that the destruction 

 of the adult does not necessarily annihilate the race. During the next two 

 months, no Lucernarians are to be found ; but in the last of August I have 

 collected young ones, much less than ^§ of an inch in diameter. 



f Haliclystus auricula, H. J. C, Journal Boston Soc. Nat. Hist., March 

 1863, p. 55y. 



X The original figure by Rathke (Miill. Zool. Danica, iv. 1806, pi. clii.), 

 although sufficiently correct for identification, can neither be called cha- 

 racteristic nor graceful as far as attitude is concerned. 



