350 SUMMARY OF CURRENT RESEARCHES RELATING TO 



e. Crustacea. 



Gall-forming- Crab.* — F. A. Potts discusses the genus Hapalocarcinus, 

 which includes crabs very small in size and profoundly modified, owing 

 to the fact that they pass the greater part of their lives confined in small 

 cavities in coral colonies. At an early age the crab settles between two 

 branchlets, usually terminal, and so influences their further growth that 

 they broaden, and, later, unite to form the so-called gall, about the size 

 of a hazel-nut. In all cases (on Pocillopora) the gall appears to be 

 formed and inhabited by a solitary female individual. At first she is 

 little more than a millimetre in carapace length. 



After opening a hundred galls without success, Potts at length found 

 the male, which is about 1 mm. in carapace length. He is free-living and 

 visits the females while the gall is still open. After fertilization, the 

 gall closes up so far that the visits of other males are prevented. 



The crab is Hot a parasite on the corals. It must live on small 

 organisms drawn in with the respiratory current. It is probable that 

 the organisms of the " nanno-plankton " (less than 3-4 //. in measurement) 

 are collected in the first place by the close-set combs of setse springing 

 from the interior of the palps of the maxillipedes which cover the whole 

 of the buccal area. 



Process of Fertilization in a Crab.| — R. Binford describes the 

 germ-cells and the process of fertilization in the edible crab, Menippe 

 mercenaria, found along the southern part of the Atlantic coast of the 

 United States. The seminal elements arise from a single row of 

 spermatogonial cells, which persist along one side of the testicular 

 tubule. The tubule is divided into three or four regions by longitudinal 

 partitions of epithelial cells. The seminal elements in one end of a 

 given division are more mature than those in the other end. The 

 spermatogonial nuclei lie in a common cytoplasmic mass, and multiply 

 irregularly without the formation of a spireme. A spireme and synapsis 

 occur in connexion with the first mitotic division. The second mitotic 

 division follows soon after the first. In the mature spermatozoon the 

 protoplasmic portion containing the nucleus is cup-shaped. From the 

 rim of the cup pseudopodia project like the rays of a star. There is a 

 capsule half embedded in the cup. An mturned tubule is connected 

 with an opening in the distal portion of the capsular wall, and a rod- 

 like central body arises from the proximal side of the capsule and pro- 

 jects into the inner tubule. In the transformation of the spermatid the 

 nucleus becomes uniform in consistence, reduced in size, and cup-shaped. 

 A mitochondrial ring is formed between the nucleus and the capsule. 

 The capsule arises as a vacuole in the cytoplasm. The central body 

 develops from a granule which appears on the proximal side of the 

 capsule. The inner tubule is formed from two vesicles which arise at 

 the distal end of the central body. Certain stimuli, such as hypotonic 

 solutions of various salts, cause a lengthening of the central body, an 

 eversion of the tubule, and an inversion of the wall of the capsule. When 



* Proc. Cambridge Phil. Soc, xvii. (1914) pp. 463-5 (3 figs.), 

 t Journ. Morphol., xxiv. (1914) pp. 147-?1 (9 pis.). 



