17 



DEVELOPMENT 

 THE EGG 



The eggs found in the plankton were identified as those of E. superba by comparison 

 with others shed by gravid females, which from time to time were kept in tanks on 

 board the R.R.S. ' Discovery II '. The appearance of the eggs is sufficiently distinct to 

 enable them to be picked out with comparative ease from the plankton samples. They 

 measure o-6 mm. in diameter when unpreserved, but after formalin has been used 

 there is a decrease in size; for example the average diameters of two batches of a 

 hundred each from two different catches at St. 540 were respectively 0-56 and 0-59 

 mm. The average sizes obtained from smaller numbers agree closely with these figures. 

 The eggs are opaque and rather densely granular ; in reflected light their milky white 

 appearance helps greatly to distinguish them. There is a thin, transparent, unsculp- 

 tured membrane investing the contents of the egg, the latter completely filling the 

 egg-shell. The average size of the eggs and the depths at which they are found do 

 not seem to be correlated. 



At St. 356, 10. ii. 30, 250-100 m., ninety-five adult E. superba were obtained in the 

 70-cm. net, although none were caught in other nets either vertical or oblique. Most 

 of the females were gravid, with spermatophores inserted in the thelycum. Four gravid 

 females were placed in an aquarium, and on the following day the distension of the 

 cephalothorax had subsided and a number of eggs were found in the water. On dis- 

 secting a female many eggs were found floating in a milky fluid which appeared to con- 

 sist of an emulsion of tiny oil globules. The eggs were of the same size as those in the 

 aquarium, namely o-6 mm. diameter. 



At St. 548, 21. xii. 30, 102-0 m., eighty E. superba were taken, among them several 

 gravid females. Two of these females were placed in a vessel containing sea water on the 

 upper bridge of the ship, and on December 23, between 2 and 4 a.m., both shed their 

 eggs. The females did not cast their skins beforehand and one still had the spermato- 

 phores in situ. On December 29 the female without spermatophores died and the other 

 died on the following day ; neither had moulted. 



Six gravid females were kept alive from St. 602, 19. i. 31, i lo-o m., and in due course 

 eggs were deposited, but attempts to induce segmentation were unsuccessful. The eggs 

 were divided into batches and subjected to varying degrees of temperature. Some were 

 kept in an aquarium at laboratory temperatures, some in a plunger jar on deck at air 

 temperature, and others in a vessel surrounded by lumps of ice. In all the experiments 

 the water was filtered before the gravid females were placed in it. 



Eggs occurred in the plankton showing all stages of development, culminating in the 

 clearly distinguishable form of the ist Nauplius, this latter completely filling the interior 

 of the egg capsule. 



