366 



SCIENCE 



[N. S. Vol. XXXIX. No. 1001 



lower lateral premolars; (13) lower second 

 molars; (14) upper second molars; (15) lower 

 third molars; (16) upper third molars. 



The law of eruption is as follows: There are 

 one or more periods of acceleration alternating 

 with periods of retardation in the development of 

 any one of the structures of the body. The peri- 

 ods of acceleration in the development of one 

 structure may be synchronous with the periods of 

 retardation in. the development of another struc- 

 ture. Thus the period of the first six months 

 after birth is one of rapid growth of the body in 

 length, and this is followed by a period of com- 

 parative rest of the body while the eruption of the 

 temporary teeth is taking place, all of which are 

 through the gums by the end of the third year. 

 This activity in dental growth is followed by a 

 period of rest. Following this there is a second 

 period of rapid growth in stature, subsequent to 

 which the permanent teeth begin to erupt, after 

 which the growth of the body is again accelerated, 

 to be followed by a second rapid eruption of the 

 permanent teeth and then another rapid growth of 

 the body which is succeeded by puberty. The 

 temporary teeth of the Americans are worse than 

 those of the Filipinos which are worse than those 

 of the Germans. The girls have worse teeth than 

 the boys in all groups. The eruption of the teeth 

 is one of the most exact means of determining the 

 relative development of the individual and may be 

 used as a physiological standard to determine the 

 relative development. 



Some Curious Parasites, Commensals, etc., Found 

 on Alcyonaria: C. C. Nutting. 



1. Discussion of the meaning of terms used to 

 indicate the associations of animals discussed in 

 the paper, and the analogies found in the Alcyo- 

 naria to plants. 



2. Commensals found on Alcyonaria.. (a) Those 

 which are apparently harmless and do not modify 

 the structure of the hosts. Illustrated by basket- 

 fish, serpent stars and mollusks. Similarity in 

 colors to the hosts. Possible advantage of associa- 

 tion to commensals. (b) Those which directly 

 modify the structure of the host, but do not sub- 

 sist upon its tissues. A genus (Calypterinus) 

 founded on such modification. Stenella kelmin- 

 thopJwra, in which the scale-like spicules have been 

 remarkably modified to form a refuge for an 

 annelid. Calyptropliora ijimw, in which a web- 

 like membrane including numerous spicules is 

 formed by an annelid. Echinogorgia pseudosas- 

 sapo, in which a barnacle has produced gall-like 

 swellings in which it finds protection. Soleno- 



caulon, in which it is claimed the leaves are modi- 

 fied to form arcade-like retreats for a macrouran 

 crustacean, and, in another case, a brachyuran. (c) 

 True parasites, apparently subsisting in part or in 

 whole on the tissues of the host. Chrysogorgia ar- 

 horescens with polyp bodies enormously enlarged by 

 a parasitic crustacean of degraded type. Suberia 

 excavata, in which the axis cylinder is extensively 

 tunneled by a bivalve, and in which a degenerate 

 annelid has also been found. (d) Parasites which 

 do not live upon the tissues of the host, but which 

 destroy it by strangulation. Millipores entirely 

 covering an alcyonarian colony. Colonial ane- 

 mones entirely covering a colony of Caligorgia 



An Experimental Comparative Study of the Be- 

 liavior of the Animals of Two Aquatic Animal 

 Communities: Victor E. Shelfoed. 

 The rapids and pool communities have been com- 

 pared. The rapids community is characterized as 

 positive to strong current and negative to sand 

 hottom, while reaction to light, contact and gravi- 

 tation are in accord with the position in which the 

 animals live, i. e., whether on, under or among 

 stones. The pool community is positive to sand 

 bottom, but only in part positive to current. It 

 differs from the pool community in reactions to 

 all the factors used. Those animals that are posi- 

 tive to current have a different optimum, hence 

 animal communities differ in their behavior reac- 

 tions. 



Are the Preotic Myotomes of the Vertebrate Head 



Post otic in Origin? H. V. Neal. 



The assumption of an exogenous origin of the 

 otic region by Piirbringer ('98) and for both post- 

 otic and preotic regions by McMurrich ('12) — ap- 

 pears untenable in the light of the evidence. As 

 pointed out by Johnston ('05) Ftirbringer 's in- 

 ferences appear fallacious as a result of his fail- 

 ure to appreciate the relations of the nerve com- 

 ponents in the occipital region. The main support 

 for McMurrich 's conclusions is therefore rendered 

 doubtful. While the relations of the posterior 

 rectus muscle of the eye to a postotie nerve — the 

 abducens — might appear to favor the postotie 

 derivation of that muscle, the relations of the re- 

 maining eye-muscles to nerves having preotic 

 niduli do not support this opinion. Moreover, if 

 McMurrich 's assumption were true, it would ap- 

 pear necessary to assume the migration of so- 

 matic motor niduli from postotie into a preotic 

 position and the associated migration of the man- 

 dibular and hyoid arches with which the myo- 



