10 Prof. R. Kossmann on the Cryptoniscidse. 



simple dimorphism of the sexes is, however, also obtained. 

 If I assume (quite arbitrarily) that the individual occupies a 

 week from hatching to male maturity, and then three weeks 

 from hatching to female maturity, then to obtain 10 (or n) 

 broods in the case of dimorphism, 10 (or n) individuals must 

 escape all the dangers that threaten them each for a week, 

 and 10 (or «) individuals each for three weeks (40 or 4n 

 weeks), while in the case of protandry only 10 (or n) indivi- 

 duals need to exist each for three weeks and 1 more for one 

 week ( = 31 or 3n + l weeks). And the advantage is even 

 still greater than these numbers show, as it is precisely the 

 first week in which the animal (in our case) swims freely 

 about, and consequently is much more exposed to dangers 

 than during the next two weeks, when it is already adherent. 

 Those 9 (or n — \) weeks which in our example are saved by 

 protandry are, as one may easily convince one's self, all first 

 weeks of life. It is the first week, that of the free-swimming 

 stage, of nine female individuals that is saved. 



The notions as to the nature of the brood-cavity in which 

 the ova in the Cryptoniscidte are sheltered until hatching 

 have hitherto been very defective. Buchholz* found that 

 in Ci^yptothir halani the deposited eggs " float to and fro . . . 

 apparently free in the body-cavity ;" but in reality are " en- 

 closed in a special, extremely delicate-walled, and perfectly 

 transparent vesicle." His further statements upon this subject 

 do not seem to me very clear. He finds this vesicle attached 

 to the outer wall of the body at the spot *• at which the four 



genital apertures are situated If we separate the 



pedicle of the vesicle from this spot we obtain it in connexion 

 with the four oviducts, which remain attached to it uninjured, 

 and the outer extremities of which seem to pass directly into 

 the vesicle." Thus, while Buchholz originally saw the ovi- 

 ducts open outwards, he sees them afterwards open into the 

 vesicle ; both observations which I can confirm as correct. 

 In spite of this the original four sexual apertures are said to 

 persist on the outer surface. " Nevertheless," he says, " the 

 presence of external sexual apertures at this spot, simultane- 

 ously with the opening of the oviducts into the egg-reservoir, 

 is difiicult to understand." In my opinion, it is not to be 

 understood ; and his attempted explanation, which I shall not 

 reprint here, is quite unintelligible to me. The true condi- 

 tion of things in Gryptotliir^ as I have observed with certainty, 

 is, that there is a sinking in of the region of the genital aper- 

 tures, at first in the form of a transverse groove. In this way 



* Bucl)linlz,/oc. cit. p. 31o. 



