ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 485 



constant presence of what seems to be a rudimentary posterior entero- 

 coelic outgrowth, of importance in connexion with the question of the 

 origin of the coeloms. The main enterocceles arise often, if not always, 

 by a single outgrowth. There is very frequently a double hydropore in 

 the early larvae. The special characters of the brachiolaria are defined. 

 The late larva is provided with a system of neuro-muscular and neuro- 

 epithelial fibres. Larva? with double hydroccele are described and their 

 morphological import is discussed. 



Asteroid Larvae.* — James F. Gemmill describes a new brachiate 

 Asteroid larva, which he names Brachiolaria hibemica sp. n. The brachia 

 are stout and columnar, with very slightly convex ends, each of which 

 carries about twenty papillae. The sucker is much elongated trans- 

 versely ; a single row of six or seven papilla? is present on each side 

 of the sucker ; there are no papilla? on the sides of the brachia ; the 

 ciliated processes are cylindrical at their extremities. It was taken in 

 a net drawn up from 1150 fathoms to the surface, 50 miles N. by W. 

 of Eagle Island, West of Ireland. A figure is given for the first time 

 of the advanced bipinnaria of Luidia ciliaris, and details are supplied as 

 to the number -and arrangement of the ciliated appendages, and the 

 dorsal and ventral median lobes. 



Double Hydrocosle of Starfish Larva. f — J. F. Gemmill discusses 

 the occurrence of a right as well as a left hydroccele in the larva of 

 Asterias rubens. The presence of two stone-canals, pharyngeal cceloms, 

 and axial organ rudiments, and their relation to one another and to the 

 mesial dorsal sac, afford confirmation of the view that the homology 

 between Balanoglossus and Echinoderms extends to many details of 

 structure. According to this view, the dorsal sac is the equivalent of 

 the pericardium in Balanoglossus, while the axial organ and pharyngeal 

 ccelom are equivalent respectively to the left pharyngeal efferent vessel 

 and the left pharyngeal ccelom of Balanoglossus. 



Cultures obtained from artificial fertilizations, and reared by feed- 

 ing with Nitschia, showed far greater numbers of larva? with double 

 hydrocceles than occur in nature. Hurried maturation of nucleus and 

 cytoplasm of the ova, and unnatural nutrition of the larva?, may induce 

 developmental instability, and the tendency to double hydroccele may 

 be atavistic. Perhaps, also, there is a " primary " homceotic tendency to 

 bilateral symmetry. There is also a somewhat different homceosis, 

 which may be described as " secondary" or " casual," manifesting itself 

 later in development, getting the opportunity to do so through failure 

 of a particular difference between the right and left sides to become 

 established at the proper time, development thereafter proceeding on 

 the same lines on both sides. The initial failure may be due to environ- 

 mental causes, which in the case of double hydroccele seem to be con- 

 nected with nutrition. At a certain stage the right middle ccelom may 

 be left isolated posteriorly like the left middle ccelom, from a cause 

 proximately connected with nutrition, and thereafter, through secondary 



* Proc. Roy. Phys. Soc. Edinburgh, xix. (1915) pp. 191-99 (1 pi.). 

 t Quart. Journ. Micr. Sci., lxi. (1915) pp. 51-80 (2 pis.). 



