20 Papers from the Department of Marine Biology. 



am not able to say whether any stage resembling the Nauplius is passed 

 through within the egg membranes, but think it is unlikely. 



I figure here a "pro-Cypris" stage (text-figure 10) where the typical 

 form of the Cypris has been attained, but the secretion of chitin has 

 only just commenced and so the appendages have not assumed their 

 articulate form. The embryonic antennae are much larger in size than 

 their ultimate development would lead one to expect. 



The Cypris larva (text-figure 11) has rather a broad, squat form com- 

 pared to that of other Rhizocephala. As Hafele has pointed out, it is 

 very much reduced in organisation. The antennae appear to lack 

 the "appendices sensoriels," which in Sacculina are used for anchoring 

 the larvae to the hairs of the host. The distal article of the antenna 

 is very small and the cement glands which might supply a secretion for 

 fixation were not seen in the Iarva3 examined, so that it is not clear how 

 attachment is effected in the first place. All these points in Hafele's 

 description are borne out by my material. It is supposed by Hafele 

 that attachment takes place on a freshly moulted crab, for the occur- 

 rence of external sacs on the hairless parts of the carapace must be 

 explained in this way, according to the development in place theory; 

 but since this theory is no longer tenable, we are left with the onus of 

 explaining attachment in some other way. It is possible that cement 

 glands are really present, but are seen only with difficulty in preserved 

 material. 



THE CHANGES IN THE VISCERAL MASS DURING DEVELOPMENT. 



As development proceeds the larvae take up more room, the egg mem- 

 branes in which they are contained stretching with their growth. The 

 interstitial cells appear to decrease in number and in the later stages 

 the interior of the visceral mass consists of a mosaic of developing 

 embryos, all in contact with small numbers of interstitial cells in the 

 gaps between the egg shells. The mantle, too, as the result of the 

 pressure of the embryos, becomes a very thin layer of tissue. 



There is, however, a definite organ in the centre of the visceral mass 

 which makes its appearance at this stage and retains its individuality 

 until the larvae hatch. This is a long thin process, the continuation of 

 the peduncular tissue, and it is hardly to be doubted that its function 

 is to supply nourishment to the developing eggs. (It is very well 

 figured in Hafele, 1. c., Taf. 2, Fig. 14, schw.} Coutiere says, in refer- 

 ence to it, that it represents the whole visceral mass; he regards the 

 developing eggs as now occupying the " mantle cavity" (cavite incu- 

 batrice), while the ovarian epithelium has entirely disappeared. As 

 stated above, the mantle cavity has no real existence in Thompsonia, 

 and in young specimens it is not simply the matter of an ovarian epi- 

 thelium, but the ovary occupies almost the whole of the visceral mass. 



