5 o8 THE AMERICAN NA TURALIST. [\'(JL. XXXV III. 



the other three being thrown off as polar bodies and later 

 degenerating. 



The Laincllibranch Xcrvous Systcin: Gilman A. Drew, 

 University of Maine.— The nervous system of the giant scallop, 

 Pectcn tcnnicostatus, is greatly specialized, and the size of the 

 animal makes it possible to study it by dissection as well as by 

 serial sections. The cerebral and pedal ganglia are small, owing 

 no doubt to the reduction of the parts they supply, and the 

 visceral ganglia, supplying the large adductor muscle and sending 

 a large number of nerves to the borders of the mantle, are very 

 large and composed of distinctly marked regions. The pallial 

 nerves that follow along the borders of the mantle lobes near 

 the bases of the tentacles and eyes, present the structure of 

 ganglia and supply nerves to the tentacles and eyes, which are 

 very abundant in this form. The need for such ganglia is 

 apparent, and their presence instead of a further complication of 

 the visceral or cerebral ganglia indicates the ease with which 

 such centers may be established when need arises. 



The fact that the pallial nerves, that here show the structure 

 of ganglia, are joined at intervals for nearly their whole length 

 by nerves from the visceral ganglia, while only a very few nerves 

 are sent to them from the cerebral ganglia, and these only to 

 their extreme anterior ends, is taken as an indication that the 

 loss during development of the anterior adductor muscle is 

 accompanied by a suspension in the growth of other anterior 

 portions, and that the bulk of the animal if formed by the 

 excessive growth of the posterior portions. 



The relation of the nervous systems of other lamellibranchs 

 was also discussed. 



The Early Stages in the Devchpment of Ophiothrix Fragilis : 

 K. W. MacBride, McGill University.— Comparatively few and 

 scattered notices are to be found in zoiilogical literature with 

 reference to the early development of Ophiuridea and in a pre- 

 liminary notice like the present communication, it will only be 

 necessary to refer to one of them. In 1891 Russo ^ published 



