106 GEOEGE W. FIELD. 



time most favorable for finding an abundance of sexually ripe 

 starfish at Wood's Hall is the month of June and in early 

 July. The larvse are to be found in considerable numbers at 

 the surface during June^ July^ and August. Those thus ob- 

 tained were immediately examined, figured as live objects, and 

 then killed separately and hardened for sectioning. All the 

 stages of larval development have been studied (1) in the living 

 condition ; (2) as total preparations ; (3) the results confirmed 

 by sectioning. For killing I found that Kleinenberg's picric 

 salt gave the most satisfactory results, particularly in the 

 younger stages. Flemming's, followed by Merkel's fluid, gave 

 excellent results, as did also Perenyi's fluid. Oil of cedar or 

 of origanum proved most satisfactory for clearing. 



Oogenesis. — The ovary is a very large compound racemose 

 gland, with a great number of spherical alveoli. When sexu- 

 ally mature it completely fills up the cavity of the arm. 

 Its colour at this time is a delicate tint of salmon. In a 

 cross-section of an alveolus is shown an external covering, 

 the peritoneal membrane, consisting of a single layer of cubical 

 cells (fig. 1, p. e.). Next, internal to this, is a muscular layer 

 of considerable thickness (m.). This is made up of fibres run- 

 ning in every direction; the outer and inner parts, however, 

 are made up chiefly of fibres running nearly at right angles to 

 each other. Within this muscular layer, and lining the lumen 

 of the alveolus, is the germinal epithelium [g. e.), showing 

 cells in various stages antecedent to their separation to form 

 ova. In the earlier stages the size of the nucleus is large in 

 proportion to the cytoplasm, but later the cytoplasm increases 

 very rapidly. In fig. 1 the lumen is completely filled with 

 mature eggs, which have assumed various shapes from mutual 

 pressure. The spaces between the ova are filled by branching 

 cells and fibres of connective tissue. Each egg has a tliiu 

 gelatinous ^external membrane, which ujjon contact with the 

 water swells by imbibition to a considerable thickness. 



The condition of the ovary a few weeks after the discharge 

 of the eggs is shown in fig. 2. The lumen is seen to be tra- 

 versed by the radiating branched cells, while the germinal 



