566 CKKSSWKLt, SHEARKIJ. 



This cuticle has been noticed by Stossich (39), Conn (9), and 

 Hatschek (17) ; the fii-st of these investigators observed that 

 it became tlie cuticle of the hirva. A simihir tliougli some- 

 what thinner membrane surrounds the eg-ys of Podarke. 

 In Serpulaitis even thicker than inEupomatus, where 

 at the animal pole it leaves quite a space surrounding the 

 polar bodies. A smaller space is found in Eupomatus, in 

 which two dark polar bodies are seeu. There is no micropyle, 

 and the sperm seems to be able to penetrate the membrane 

 at any point. 



It must be remembered that the type of cleavage of such 

 widely separated forms as Hydroides, Thai as se ma, 

 Podarke, and Lepidonotus resemble one another on 

 account of their possession of a trochophore. They all 

 possess a free-swimming stage of considerable duration, and 

 as the initial size of the blastomeres stands in direct relation 

 to the size of the part to which they give rise, as pointed out 

 by Lillie (25), the resulting cleavage conforms to the same 

 type. 



4. Seg.mkxtation and Gastkulatiox. 



Segmentation begins about one to two hours after the sperm 

 have been added to the eggs. The rate of development 

 naturally varies greatly, being increased with any rise and 

 decreased with any fall in the temperature. With the hot 

 weather in Naples during the summer months, development 

 quickly becomes abnormal unless precautions are taken to 

 keep the water cool in the culture dishes. Segmentation is 

 rapid and regular once it has set in, and results in a blastula 

 containing a segmentation-cavity of variable dimensions, it 

 is of the equal type, and i-esembles very closely that of the 

 Annelid Podarke, which is remarkable for the fact that 

 the spiral symmetry is i-etained almost complete up till an 

 unusually late stage. The first cleavage furrow cuts through 

 the egf^, sinking in more rapidly at the upper than at the lower 

 pole, and produces the two-cell stage. The first cleavage is 



