Note on Piona carnea and Eurycypris pubera. 93 



get the eggs on to this track ; in a few cases the eggs rolled off and fell 

 within the shell of the ostracod. These eggs hatched out in six to seven 

 days, hut I could not see that the larvae caused any damage to the 

 eggs or developing larvae of the Hydracarid, which did not emerge until 

 two or three days later — the total period in their case being twelve to four- 

 teen days. While some of the patches of eggs hatched out, others did not 

 get a chance. I found that though several of the Eurycypris were occupied 

 in depositing their eggs, others of the species were as busily occupied in 

 devouring the gelatinous matrix and with it the hydracarid eggs embedded 

 therein. The assiduity with which this was done, particularly where the 

 eggs were concerned, suggested to me that this must have been palatable 

 food for the Ostracods. Nor were the ostracod eggs exempted from the 

 destruction, since only a thin film remained on the glass to mark the place 

 where the mass had been. It is thus evident that the gelatinous matrix 

 which covers the hydracarid eggs and attaches them to some object during 

 the period of incubation does not afford them a complete protection. 



Though some of the egg clusters were completely destroyed, others were 

 only partially so, and I was thus enabled to isolate a number of the develop- 

 ing larva? of Piona carnea in the deutovum stage. A number of these had 

 attached to them, in some cases anteriorly and in others posteriorly, half of 

 the first covering or egg shell, and I was thus enabled to see how the 

 deutovum was freed from this. When describing the species examined by 

 him, Claparede figured the shell in one case as rupturing longitudinally and 

 in another case obliquely. Kramer also describes the rupture as oblique. 

 In the case of Piona carnea, I found the hyaline shell had ruptured 

 transversely and from its subsequent behaviour I judge it to be somewhat 

 elastic. So long as the Embryo retains its globose form, the two hemispheres 

 of the original egg shell will remain attached. As the creature develops it 

 assumes a flatter form, thus relieving the pressure which keeps each hemi- 

 sphere distended and allowing each to slip off from the deutovum. Each half 

 of the shell then collapses into the form of a semicircle having a double 

 membrane stretched within its curvature. The curved margin straightens 

 itself out in a short space of time, and as it does so the membrane stretches 

 and rolls its free edges back until the whole assumes a lanceolate shape. 

 These lanceolate figures are to be seen in the gelatinous matrix during the 

 development of the egg, and at first sight are suggestive of diatoms lying 

 among the eggs. The larva? were all too far developed to permit observation 

 of their earlier stages, but I had opportunity to observe their behaviour from 

 the time when the power of movement was first manifested. At first a 

 faint twitching of one pair of limbs only was apparent. After an interval 



