PHYLUM ANNELIDA. 



JL 



st 



When the eggs of an earth* 

 worm are liberated, they are 

 surrounded by a sheath of 

 gelatinous stuff, believed to 

 be secreted by the saddle. 

 As this is peeled off towards 

 the head, spermatophores are 

 also enclosed. 



Development. Many 

 cocoons are made about the same 

 time, and each contains numerous 

 ova, and also packets of sperms, 

 so that fertilisation takes place 

 outside the body. These cocoons 

 are buried in the earth a few 

 inches below the surface. They 

 measure about a quarter of an inch 

 in length. 



The favourite time for egg- 

 laying is during the spring and 

 summer, thoug-h it may be con- 

 tinued throughou 4 : the whole year. 

 The earthworm of the dungheap 

 (L. fatidiis) make* this a habit, 

 induced probably by the warmth 

 of its environment. 



Of the many ova in the cocoon 

 of Z. terrestris, only one comes 

 to maturity, while in L. fcettdus a 

 few, and in L. communis two may 

 do so. But in the last species 



FIG. 114. Stages in the develop- 

 ment of earthworm. After 

 Wilson. 



1. Two-celled stage ; p.c., polar bodies. 



2. Blastula ; M., a primary mesoblast. 



3. Gastrula stage ; EC., ectoderm or 



epiblast ; /in., endodenn or hypo- 

 blast, in process of being covered 

 by the small ectoderm cells. Note 

 the widely open blastopore ; M. t 

 mesoblast cells. 



4. Longitudinal section in late gastrula 



stage, showing germ -bands; ec., 

 ectoderm; en., endoderm ; M., 

 mouth ; st., stomodaeum ; m., 

 primary mesoblasts ; Nb., neuro- 

 blasts; nc., nerve-cord; N., ne- 

 phridioblasts ; ms., mesoderm 

 bands ; npc., incipient nephridia. 



