\Q2 Parasites of the Parasites. 



These larva e then are ali functionally males, but those that are fixed to Sacculina 

 or Inachus, as opposed to those which are crawling on adult Danalia, have ceased to function 

 as males and have already begun to develope into females. Ali the larvae, however, examined 

 by me which had recently' attached themselves to the host, stili contained some sperm, and 

 in several cases a great quantity of sperm was stili present. 



Piate 7 fig. 25 is a transverse section through the body of a Cryptoniscus larva which 

 has already become fixed to a Sacculina. The testis is seen to stili contain some sperm, but 

 it is now mostly composed of a coagulated fluid. The phagocytic cells (n) are seen to be in 

 the act of absorbing this fluid, which in their neighbourhood is being converted into drops 

 of liquid that are engulphed into the cell-bodies. 



In the anterior region of the sexual gland, a section through which is shown in Fig. 26, 

 the developing ovaries (ov) are seen as two caps of small cells on the dorsal surface, lying 

 above the most anteriorly placed phagocytic cells. 



The parasite now loses ali trace of its early male nature, and has the form shown in 

 figs. 27 and 27 a. The proboscis (pr), which has greatly elongated, is fixed far into the tissues 

 of the host. The gut is sack-like and greatly swollen. A conspicuous heart (h) is seen pul- 

 sating in the posterior region. The ovaries (ov) lie on the dorsal surface as narro w strips, while 

 laterally the phagocytic cells (n) are seen as refringent masses. Fig. 27 a Piate 7 is an optical 

 section of a whole preparation, which shows very clearly the relations of the various parts, 

 especially the hugely developed phagocytes. A transverse section through the body at this 

 stage is shown in Fig. 28, in which the ovaries are clearly shown, and also the phagocytic 

 cells (n) with darkly staining cytoplasm and degenerating nuclei. These phagocytes, after per- 

 forming their function of absorbing the remains of the testis, do not appear to fili any further 

 róle in the economy of the animai. At first they increase greatly in size and in number by 

 amitosis, but as soon as the fixed parasite begins to grow large, degenerative processes rapidly 

 set in. The cytoplasm becomes loaded with chromatic granules derived from the degenerating 

 nucleus, and in the adult parasite the remains of the phagocytic cells are seen as darkly 

 staining rings of protoplasm from which ali trace of a nucleus has disappeared , leaving a 

 clear hollow in the centre (n Fig. 29). I am inclined to notice a dose parallel between these 

 phagocytic cells and the hypertrophied cells of the testes of the Pdiizocephala described in 

 Chapter 2. That the germinai cells of the testes of two such widely separate hermaphroditic 

 forms should undergo similar processes of degeneration, is highly suggestive. 



The rest of the life history is taken up, firstly, in the rapid growth of the ovaries, 

 which, absorbing the nutriment from the inflated gut, come to fili up the whole of the body 

 cavity, and secondly in the act of fertilization. The spermathecae, which Fkaisse (1) de- 

 scribed as gills, are present in the adult as two pairs of ramifying organs on the ventral sur- 

 face with their external openings protected by chitinous appendages. They are each composed 

 of two parts, a part opening to the exterior lined with a regular epithelium, and an internai 

 lacunar portion in which the spermatozoa after coition may be found lodged. Fig. 29 Piate 7 



