370 DR. W. M. TATTERSALL ON THE STOMATOPODA AND 



noted above appear to show a close parallel to the case of A. polymorplius. 

 The small male (No. 3) probably corresponds to Kemp's form I., and the 

 males 4 and 5 to forms II. and III. The want of the full complement of 

 limbs precludes an absolute comparison. 



But the small male, form I., was taken in the company of an ovigerous 

 female and therefore in the breeding-season. It is possible that the capture 

 was made at the very beginning of the breeding-season before this male had 

 moulted into its full adult stage. But another explanation of the facts 

 suggests itself. Kemp notes that in all the forms the appendix masculina on 

 the second pleopods was well developed, and the same observation applies in 

 the present case. I suggest therefore that form I. is a breeding phase and 

 that Aihanas becomes sexually mature before it is fully grown. This would 

 explain the full development of the appendix masculina and receive support 

 from the capture of a form I. male in the breeding-season. We may turn 

 to the Amphipoda for the necessary analogy. 



Walker, in a paper ".Notes on Jassa falcata (Mont.)" (Proc. Trans. 

 L'pool. Biol. Soc, vol. xxv. pp. 67-72, 1911) calls attention to an interesting 

 series of facts. In a single gathering of Crustacea made from a buoy 

 moored in the harbour of Port Erin, he found an enormous number of 

 specimens of the Amphipod Jassa falcata which could be divided up into 

 groups. The circumstances of their capture and the area of their occurrence 

 afford the strongest evidence that all the specimens belong to one species. 

 Walker found two groups of ova-bearing, i. e. sexually mature, females 

 differing not only in size but in the form of the gnathopods. In other 

 words, here is evidence that Crustacea may be sexually mature though not 

 structurally fully grown. A similar phenomenon is not so easily demon- 

 strable for males except by sections, but, given its occurrence in females, 

 there seems to me to be no inherent difficulty in accepting its occurrence in 

 males. Walker also found three forms of males which he interprets as a 

 penultimate form and two forms of the fully-grown male, into one or other 

 of which the penultimate form moults. 



We have in this case, I think, an interesting parallel to what Kemp has 

 observed in Athanas 'polymorplius, and to what probably occurs in Athanas 

 djiboutensis so far as the imperfect specimens at my disposal can be 

 interpreted. 



Walker's evidence, coupled with the occurrence of a form I. male of 

 A. djiboutensis in the breeding-season and the well-developed appendix 

 masculina present on all three forms of male, has led me to suggest that 

 Kemp's observations may be explained on the following grounds : — that all 

 three forms of male are breeding forms, that form I. is sexually mature but 

 not structurally fully grown and eventually moults into either form II. or 

 III., which are truly dimorphic forms of the fully-grown male. From the 



