4 8o 



HISTOLOGY 



ing. Some leeches also form double spermatotheca as described by 



Whitman. 



The most complicated, exact, and highly specialized of the male 



nidamental-tissue products is to be seen in the spermatophores of certain 

 cephalopod mollusks. This beautiful mechan- 

 ism is produced in a differentiated portion of 

 the seminal duct. This differentiated region 

 consists of four divisions of the seminal tube. 

 A prostate gland described in an unpublished 

 work by L. W. Williams as a compound lamel- 

 lar gland, and a glandular caecum take part in 

 the formation of the spermatophore. The exact 

 manner, however, in which the structure is 

 formed is not known. Figure 451 gives some 

 \n| idea of its complexity and of the delicacy of the 



processes by which it was formed. 



In the female, the number, complexity, and 

 peculiar distribution of nidamental structure is 

 a formidable obstacle to a short and compre- 

 hensive account of them. As has been said, 

 some comparatively few forms discharge the 

 eggs externally in a fluid. And again, some of 

 the highest forms which develop the ova inter- 

 nally, do so without the aid of any shell or fluid 

 envelopes whatever. The follicular and ccelo- 

 mic discharging fluids have already been men- 

 tioned in the remarks on that subject. 



The planarian worms make cocoons in the 

 uterus by depositing a chitinous envelope 



FIG. 451. View of the central around the ovum. In some forms this cocoon 



The mass of spermatozoa by which it is attached, as a stalk, to rocks, 



trate the exact and finished these cocoons are secreted by the columnar epi- 



Among some other worms can be found 

 fairly well specialized nidamental tissues. Two of these, the earth- 

 worm, Lumbricus, and the leech, Pisicola, show interesting and typical 

 forms. 



The specific cells of both of these organs are modified mucous cells, 

 which have probably been evolved from the ordinary epithelial mucous 

 cells, such as are to be seen in the covering epithelium of the earthworm. 



The nidamental cells of Pisicola lie inside the body cavity, or, to be 



