April 11, 1902.] 



SCIENCE. 



579 



arches being derived from the ventral mes- 

 oderm and the remaining cranial muscu- 

 lature from the dorsal mesoderm. It is 

 noteworthy that the branchial musculature 

 is supplied by lateral motor nerves and by 

 these alone, while the dorsal musculature 

 is supplied by median motor roots. Con- 

 sequently the nerves supplied to the myo- 

 tomic muscles of the trunk are to be 

 regarded as the homologues of the cranial 

 median motor nerves, while the white rami 

 fibers, which control through sympathetic 

 neurons the visceral musculature of the 

 trunk derived from the ventral mesoderm, 

 are the equivalents of the cranial lateral 

 motor components. 



The other ideas referred to in the paper 

 may, for lack of space, be stated sum- 

 marily. (1) The distinction between vol- 

 untary and involuntary muscles is a phys- 

 iological and liistological one, and not 

 morphological, and the branchial muscu- 

 lature is morphologically equivalent to the 

 visceral musculature of the trunk. (2) 

 The branchiomeric segmentation is not 

 identical "with the myotomie, but in the 

 cranial region there exist together two dis- 

 tinct segmentations. (3) Of these the 

 branchiomeric segmentation is probably 

 the older phylogenetically. 



Geographical Distribution of Fresh Water 

 Fishes of Mexico: S. E. Meek. (Read 

 by title only.) 



Feeding Habits of a Spatangoid, Mop.ra 

 atropos; a Brittle-Star Fish, Ophio- 

 phragma Wiirdmannii, and a Holothu- 

 rian, Thy one briareus: Casvtell Grave. 

 The observations here given were made 

 on animals kept in the Beaufort U. S. P. 

 C. Laboratory in aquaria in which a bal- 

 ance had been established between animal 

 and plant life by means of diatoms. The 

 spatangoids were reared from plutei. 



The function of the so-called ambulacral 

 brushes of spatangoids, which are so con- 



spicuously waved about in the water above 

 the animals when dug up and placed in 

 aquaria, has been thought to be principally 

 a respiratory one, but I have found that 

 the animals use these brushes as hands for 

 grasping bunches of sand and diatoms and 

 carrying them to the mouth, the bristles 

 of the brush being used as fingers. 



Ophiophragma lives below the surface 

 of the sand, with the oral surface of its 

 disc and arms applied to some large object 

 and -with the tips of its arms extending 

 into the water above. The foot-tentacles, 

 distribtited in pairs along each arm, are 

 seen to be in constant waving motion, and 

 by close observation it may be seen that 

 they are busily engaged in passing little 

 pellets of sand and diatoms toward and 

 into the mouth. Down the oral surface of 

 each arm is travelling a procession of pel- 

 lets which have been gathered up by the 

 more tei-minal tentacles and which are 

 being successively handed on by the more 

 proximal pairs. 



Thyona, in feeding, fully extends the 

 long branching tentacles which surround 

 its mouth, and mops them about in the 

 sand until they are well covered with sand 

 grains and diatoms; then they are, one by 

 one, turned back and poked down the 

 throat; the mouth closes around the base 

 of the tentacle and, when withdrawn, it is 

 free from all debris. 



A Method of Bearing Marine Larvce: 



Caswell Grave. 



A method of rearing echinoderm larviB 

 which I have used for two seasons with 

 much success consists in supplying the 

 aquaria containing them with a generous 

 amount of sand containing diatoms. 



Prom twelve to twenty-four hours after 

 fertilization, the eggs reach a stage in 

 which they swarm at the surface of the 

 water. At this time it is easy to get a 

 pure culture of larva3 by skimming the 



