420 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to the axial filament, but the head undergoes three torsions in the course 

 of development which result in a variety of appearances. The intricate 

 changes of the two central corpuscles are minutely described. A head- 

 cap, formed from a vesicle of the idiozome, is a transitory structure 

 thrown off when the head takes its final form. 



Morphology of Teleostean Head Skeleton.* — H. H. Swinnerton 

 has made a study of the developing skull of the three-spined stickle- 

 back (Gasterostem aculealus). 



The cranial flexure, together with other features in the shape of the 

 embryonic head skeleton in Teleosts, is probably a mechanical effect 

 due to differences in the degree of distensibility between the dorsal 

 and ventral surfaces of the brain, and to the presence of skeletal struc- 

 tures in close association with the latter. 



The presence of an epiphysial bar, with consequent division of the 

 large dorsal cranial fontanelle into two, is a common feature in develop- 

 ing Teleosts. The Ostariophysi differ from others in retaining this 

 early condition of the cranial roof in the adult. 



The intra-cranial notochord, so far from undergoing reduction, never 

 at any stage ceases to grow. 



In Gasterosteus the elements concerned in the support of the jaws 

 and operculum, and in the attachment of the associated muscles, seem 

 to undergo a considerable acceleration in development compared with 

 the rest of the head skeleton. 



Three types of palato-ethmoidal relationship exist in Teleosts and 

 the immediately related Ganoids. The study of the structure and de- 

 velopment of the head seems to point to a common ancestral stock for 

 Elasmobranchs and Teleosts. The manner of mandibular suspension 

 in Teleosts is insufficiently described by the term hyostylic. 



The Lophobranchii and Hemibranchii together constitute a natural 

 group (Thoracostei). To these, through the Gasterosteoidei, the Scom- 

 beiesoces approach more closely than do any other living Physoclysti. 

 As judged by the study of the ethmoid and suspensorial regions, the 

 Zanclidas and AcrouuridaB are closely allied to the Plectognathi, but 

 the affinities of these forms must not be sought amongst living Physo- 

 elysti. 



Development of Inner Ear in Bat. f — P- Denis has made, with 

 particular reference to Vespertilio murinus, a detailed study of the de- 

 velopment of the external forms of the labyrinth and especially of the 

 changes exhibited by the epithelium at various stages. The successive 

 forms of the inner ear are made evident by photographs of twenty-one 

 models constructed on Bora's method. 



Migration of Eye of Flat-Fish.J— S. B. Williams has studied the 

 changes accompanying the migration of the eye in Pseudopleuronectes 

 americanus, and has made a number of observations on the tractus 

 opticus and the tectum opticum. The first step in preparation for 

 metamorphosis is the rapid resorption of the part of the supraorbital 

 cartilage bar which lies in the path of the eye. This is probably due 



* Quart. Journ. Micr. Sci., xlv. (1902) pp. 503-93 (4 pis. and 5 figs.). 



t Arch. Biol., xviii. (19U2) pp. 377-493 (7 pis.). 



X Bull. Mus. Zool. Harvard, xl. (1902) pp. 1-57 (5 pis.). 



