igoy.j Records of flic Indian Museum. 287 



parasitic hydroids deprives them of the power of catching their pre}' 

 in the manner common to all other hydroids. Their mode of life 

 is identical in both cases. Both were found adhering like a tuft 

 to the skin of small fishes which were caught near the surface of 

 the sea. Judging from Fewkes's well-executed illustration of the 

 fish with its parasite, the superficial appearance of both would be 

 very similar. 



From the relatively large size of the hydranths of Nudiclava 

 it is difficult to suppose that they are degenerate bodies of Httle 

 functional value to the colony. The peculiar features of the en- 

 doderm of Nudiclava, the well-developed muscle strands, and the 

 special pavement epithelium lining the central cavity, suggest that 

 the methods by which these hydranths obtain food is as follows : — 



It is supposed that in their natural state, they assume, by 

 expansion of the mouth, the shape of a wide-spreading funnel 

 (pi. xvi, fig. 2). As the host speeds through the surface waters, 

 the small members of the plankton, such as copepod nauplii, etc., 

 must come within the grasp of these funnel-shaped mouths. The 

 well-developed muscles, situated iii the endoderm, which are pecu- 

 liar to the genus, point to a special power of rapid and forceable 

 retraction, an act which would be very necessary when anything 

 comes within the grasp of the funnel. The special pavement epi- 

 thelium is perhaps developed as a protection and covering to the 

 endodermal cells which would otherwise be exposed to the water, 

 when the mouth is gaping widely. 



We can ihustrate the possible efficiency of this mode of food- 

 capture thus : It is not unlikely that the hydranth, which 

 measures '75 mm. in length when completely contracted, could ex- 

 pand its mouth into a circle '5 mm. in diameter The hydranths 

 in the colony, which number about 50, would together present 

 an area of about 10 square mm., which is at least as great as that 

 of the gaping mouth of the fish host itself. 



In the case of Hydrichthys , the hydranths, from their size, 

 must also be considered important members in the colony. And 

 there is some evidence in Fewkes's account that it obtains its food 

 in this manner. Thus we read above, that the free or oral ends 

 of the filiform bodies of this genus are sometimes trumpet-shaped, 

 and one of these bodies contained a mass resembling food. 

 Hydrichthys was kept alive in an aquarium for some time, but it 

 would have been impracticable to examine the colony without 

 catching the fish, a procedure which would cause at least partial 

 contraction of the parasite : consequently it would be very diffi- 

 cult to observe the state of the oral apertures in their expanded 

 condition, and the fact that some few were observed to be 

 trumpet-shaped, makes it most likely that all would possess, in 

 their expanded condition, a wide funnel-shaped mouth. 



Let us pass now to a consideration of the third genus 

 of hydroids which is found on fish. The case of Stylactis minoi 

 on the fish Minous inermis is quite different from that of 

 the others. The hydranth has a well- developed circle of long 



