588 F- ^- i'OTTS, 



eggs finallj' reach the mantle cavity, the cementing- substance solidifles 

 aud attaches the eg-gs to the mantle. ^) In this development of the 

 colleterial glands there is plainly a special adaptation for preventing 

 the emission of embrj'os during the respiratory niovements. 



In Mycetomorpha the eggs must be laid in a totally different 

 manner without ducts, and as the mantle aperture is greatly restricted 

 and the size of the eggs probably large, elaborate arrangements to 

 prevent the escape of the brood are nnlikely and unnecessary. On 

 tlie other band it is seen that the glands of Mycetomorpha are in füll 

 secretory activity just at that time when the ova are beginning 

 to grow in preparation for the production of another brood, and 

 they secrete into the cavity of the ovary and not to the exterior 

 (as do the colleterial glands of Sacculina). From these circumstances 

 I feel inclined to regard them as glands which help to nourish the 

 growing ovary, elaborating a yolky secretion. 



At the same time in their ectodermal origin, paired character 

 and histological appearance they show similarity to the colleterial 

 glands of Duplorhis and I regard it as possible that they represent 

 also the colleterial glands of the typical Rhizocephala in a greatly 

 modifled condition and with a change of function. 



The Larvae. 



The Cypris larvae of Mycetomorpha are similar to those described 

 so thoroughly by Delage (3) in Sacculina and it is not thought 

 necessary to offer here a detailed accoiint of their structure. In 

 certain features of the histology a slight difference appears. A trans- 

 verse section of a Cypris larva anterior to the region of the thoracic 

 appendages is shown in PI. 16 Fig. 10 and represents the various 

 histological Clements to be found. There is an epithelium (ep) 

 not always to be easily distinguished from the underlying reticulate 

 tissue {ret) with no cell walls and few nuclei. Dorsally are tobe 

 seen the longitudinal muscle {mu) of the limbs cut in section 

 and surrounded by a chitinous sheath. Ventrally, on eacli side, is 

 a Cluster of numerous and very small embryonic cells (using 



1) Smith (5), p. 121, tab. 8 fig. 13. 



A further safeguard against the escape of the brood during incubation 

 is the development, in Sacculina, of a special arrangement of hooks, the 

 retinacula, for fixation of the egg-tubes. 



