64 Papers from the Department of Marine Biology. 
A COMPARISON OF HAPALOCARCINUS AND CRYPTOCHIRUS. 
There is no doubt that Hapalocarcinus and Cryptochirus are very 
closely related. The same striking modifications of structure occur in 
both. Of these the reduction of the oral appendages and the gastric 
mill show a common method of feeding, while the abnormal growth of 
the abdomen is connected with the production of large broods of eggs, 
a property very necessary for a sedentary animal. The structure of 
the oral appendages and the maxillipeds is almost identical in the two 
cases (text-figure 16). The abdominal appendages, also, have exactly 
the same modifications. 
ex. mp.2 
ex.mp.1 
“4 = 
Fig. 16.—Buccal area of Cryptochirus. X 90. 
For comparison with that of Hapalocarcinus. Drawn from a specimen cleared in potash and 
mounted in Canada balsam. On one side maxilliped 3 and parts of other appendages have 
been removed; on the other maxillipeds 1 and 2 are shown occurring beneath 3. The pa- 
pille on the surface of maxilliped 3 are indicated by small circles. It will be seen that max- 
illiped 3 comes much closer to the middle line than in Hapalocarcinus and that the provision 
of setze for the exopodites of maxillipeds 1 and 2 is not marked, while they are not found on 
the border of maxilliped 3. The main work of sieving is done by the strong sete arising from 
the endopodites of maxillipeds2.and3. The sieve has not so fine a mesh as in Hapalocarcinus. 
B. mp. 1, C. mp. 2, basipodite and coxopodite of first maxilliped; mz. 1, mz. 2, first and second 
maxille. Other letters as in text-figure 5. 
Such structural differences as exist correspond to their diverse 
habitations. Hapalocarcinus affects branching corals with individual 
polyps much smaller than itself, even at the earliest stage, and forms a 
complicated gall almost completely shut off from the exterior by con- 
trolling and modifying the branching of the coral. Cryptochirus, on 
the other hand, seeks to house itself in massive Astreid corals, where 
the individual thece are of such size as to accommodate the intruder. 
It occupies a theca after passing through its larval stages and very soon 
the growth of the polyp is suppressed and death will follow. The 
