1908.] ASPIDOBRANCH GASTROPOD MOLLUSCS. 861 



of all species much resemble those of Sejitaria, but the extent 

 and shape of the ciliated tracts yayj slightly in different species 

 — not to such an extent, however, as to make it worth while 

 to write a separate description for each. 



The Hcemoccele and C(dom. 



The only noteworthy feature about the hfemocoele is that it 

 tends to be filled up by an abundant development of vesicular 

 connective tissue, which penetrates into all the spaces between 

 the viscera, except the coelomic spaces, and is specially accumu- 

 lated round the blood-vessels. It is naturally much altered by 

 the action of reagents in tropical specimens long preserved in 

 spirit, but may conveniently be studied in J\^eritina fluviatilis^ 

 As I have not yet been able to obtain Paravicini's memoir on 

 the connective tissue of Gastropods, nor have I had time to 

 make a comparative study of this tissue in freshly killed 

 specimens, I will only shortly mention the appearance presented 

 by this tissue in Neritina. In starved specimens which have 

 been kept for a long time in aquaria, the connective tissue 

 consists chiefly of a number of stellate cells united by their 

 processes, or, if one prefers to express it so, of a reticulum of 

 protoplasm with nuclei at the nodes. These nuclei (fig. 59, 

 ret^ are small, oval, and deeply staining. In well -nourished 

 specimens recently taken from the river the meshes of the 

 reticulum are filled with vesicular cells ("Laiager's cells ") with 

 larger faintly staining nuclei. These cells ai-e filled with 

 granules which stain bright yellowish green in picro-indigo- 

 carmine. They accumulate round the blood-vessels, and are often 

 so abundant as to obscure the network of connective tissue.. 

 Apparently they are derived from small amoeboid cells Avhich 

 contain similar large nuclei such as that marked am. in fig. 59. 

 There can be little doubt that these cells are metabolic in function 

 and serve to store up reserve material, though I have not been 

 able to demonstrate the presence of glycogen in them as Blund- 

 stone (5) has in other molluscs. Masses of fatty-looking tissue of 

 this nature surround the intestines, liver, nerve-cords, and even 

 the accessoiy genital organs of troj^ical species of JSferita and 

 Paranerita and their presence is a great hindrance to dissection.. 

 I have found that this tissue blackens slightly with osmic acid in 

 Paranerita, indicating the presence of fat ; and this is worth 

 noticing, for fat-cells are said to be absent from the connective 

 tissue of Gastropods. The vesicular cells of JVeritina are not 

 blackened hj osmic acid. 



The coelomic cavity is fully as extensive, and has much the 

 same relations as in Septarki, but owing to the retention of the 

 spiral coil of the visceral mass, and the complications arising from 

 the excessive development of the spermatophore-sac of the female 

 or the epididymis of the male, it is diflicult to give an intelligible 

 account of it ; but I hope that with the assistance of the diagram 



