OBSERVATIONS ON CRIODEILUS LACUUM. 557 



spermatophores in the cocoon, allows one to suppose that the 

 moulted skin of the anterior part of the body takes a share in 

 the formation of the cocoon, just as in Lumbricinse and Nephe- 

 lidae, the egg case probably owes its origin to the moulting of 

 the clitellum. Since, however, the number of bauds in this 

 egg case exceeds twenty, it is probable that the somites lying 

 behind the genital pores also take part in the formation of 

 the cocoon. 1 The tough secretion which builds up the chief 

 portion of the cocoon, is probably furnished by the large swel- 

 lings around and in front of the genital pores, and by the 

 inner lining of the sperm duct. The process of formation of 

 these egg cases, which alone would lead to positive results, I 

 have unfortunately been unable to watch. Worms which I 

 kept in my aquarium always hid themselves under cover of the 

 roots of Sium 1 at i folium, so that I was unable to overlook 

 their operations. 



A transverse section through this cocoon shows three layers; 

 an inner yellowish and homogeneous layer, an outer strongly 

 fibrous, and a middle layer of interlaced strands (fig. 4). The 

 fibrous layer is most easily seen at that end of the cocoon 

 which is drawn out into threads (fig. 2), where they are col- 

 lected together into strands and finally separate out into 

 elastic fibres ; the latter serve for attachment to aquatic plants. 

 Towards the swollen portion the fibrous layer becomes thinner 

 at the expense of the middle layer. 



The middle layer (fig. 5) consists of innumerable interwoven 

 bundles which are not separated into fibres. The network is 

 densest below and becomes looser above. It looks so very 

 much like a plant tissue, that a young botanist of this country 

 at first disputed as to the substance of the tissue. Some 

 thought it of vegetable origin. 



The lowermost or basal layer is made up of very many 

 extremely delicate strata (fig. 6) ; these show a striated struc- 

 ture, and contain here and there fibrous elements. This layer 

 projects from the free end of the cocoon (fig. 3), is strongly 

 folded, and serves to close the egg case. 



1 See the following paper, in which the Clitellum is described. — Translator. 



