xv, e Shaw: Campbellosphaera 499 



their gonidia have begun to separate, the specimen (No. 10) 

 shown in Plate I, fig. 3 was photographed. It measured about 

 280 by 295 ft, and an estimate of the number of somatic cells is 

 2,675. The figure shows the anterior pair of embryos youngest, 

 in the bullet stage. About in the equatorial plane is an anoma- 

 lous pair consisting of a gonidium in the background and a 

 more advanced embryo in the foreground. In the posterior 

 quarter of the coenobium the micrograph seems to show an 

 anomalous quartet, of which the embryo at the right is clearly 

 the most advanced in development of all in the coenobium. 

 Partly behind it appears a bullet embryo, and at the left a 

 smaller gonidium. The fourth member of the quartet must 

 have been a foreign body behind the coenobium, for now it 

 cannot even be found near the specimen. Since being photo- 

 graphed the specimen has separated from its neighbor, rotated 

 so as to present the posterior pole, and shrunken to the extent 

 of diminishing the transverse diameter from 290 fi to 214 p. 

 The gonidia show no shrinkage, but give slightly larger measure- 

 ments, which may be attributed to more careful adjustment of 

 the microscope. They are about 50 and 56 /x in diameter. 



The extent to which the daughters and their gonidia develop 

 before birth is shown in Plate I, fig. 4. This specimen (No. 11) 

 now lies in almost exactly the position in which it was photo- 

 graphed. But its dimensions have decreased from 315 by 380 y. 

 to 295 by 355 fi. The thickness of the specimen at the present 

 time measures, with an allowance of 1.4 for the optical density 

 of the Venetian turpentine, about 260 ;i, which indicates prac- 

 tically no flattening from cover pressure.' The somatic proto- 

 plasts of the mother measure about 5 //.. The characteristic 

 convexity of the outer side of the membrane of the somatic cells 

 is clearly exhibited under the microscope, especially in the optical 

 sections of the protrusions caused by the pressure of the 

 daughters. The convexity is such that the plane of the base of 

 the dome often intersects the protoplast below the middle; that 

 is, more than half of the protoplast lies within the dome. The 

 spacing of the cells is estimated to be now about 10.8 /*. This, 

 with 315 it taken as the mean diameter for the coenobium, gives 

 us 3,080 for an estimate of the number of cells. The gonidia 

 of the daughter were counted by carefully focusing with a 

 high-power objective. The daughters number 7 ; and the gonidia 

 in five of them are 8; in one, 7; and in one, 6. In four of the 



1 The cover glass is supported by glass rodlets of the following thick- 

 nesses; 346, 347, 373, and 378 /*. 



